(warning: sorted in an idiosyncratic and inconsistent way)
Ageing
Sponsor a grandparent
Animals
Adopt a gorilla
Be a friend to bees
Fight sale of animal-tested cosmetics in EU
Put food out for birds
Take old linens/towels to an animal shelter
Arts
Support an artistic project with Kickstarter
Take the time to appreciate a street performer
Books
Bring library books to a homebound person
Leave a book you love in a public place
Read a banned book
Show the MDG comic book to a kid
Business
Clean up after yourself in a store
Contact a company to say thank you, not complain
Help turn Volkswagen from the dark side
Use GoodGuide for more ethical shopping
Visit an independent business instead of a chain
Campaigning
Condemn the US funding cut to UNESCO
Share or post to the "We Are The 99%" site
Sign a petition
Children
Raise £2 for Save the Children with a click
Support the child soldiers treaty
Clothing
Buy "aftersocks" to help rebuild Canterbury, NZ
Pair up mismatched gloves
Communication
Ask "How are you" and really mean it
Compliment a stranger
Listen to someone
Send a fan letter to someone who isn't famous
Send an ecard
Thank a UN peacekeeper
Write to a political prisoner
Competitions
Counteract a negative online comment
Help publicize a great website
Help someone get online
Nag yourself into doing good
Try a new search engine
Cooking
Cook with weeds
Double up on lunch for a colleague
Get inspired by a vegan e-zine
Make a dish that reminds someone of home
Drinking
Buy Fair Trade liquor
Try to drink more ethically
Education
Donate items needed by a public school
Donate to the Scholar Rescue Fund
Give pencils by signing up for Camfed news
Exchange skills
Take action with a 10x10 partner
Thank an old teacher
Energy
Provide a solar light bulb to a Haitian family
Switch energy suppliers
Use short bursts of exercise to save on heating
Environment
Complain about excessive packaging
Copy an Earth Day pledge
Encourage the switch to paperless receipts
Plant a tree
Recycle one item you normally wouldn't
Food
Bring food to protesters or volunteers
Buy loose produce wherever you can
Buy out-of-date groceries
Cut one questionable item out of your diet
Implement a Love Food Hate Waste tip
Make healthy treats for a dieting friend
Pick some fruit
Post a recipe for ChildLine
Start a food sharing group
Treat someone to a meal
Games
Play online poker for International Medical Corps
Play WeTopia
Start a virtual tiger park
Gender
Become a member of ACWW
Shop to support female entrepreneurs
Take part in an International Women's Day event
Gifts
Exchange unwanted gifts
Give an edible mix
Give a reusable gift instead of a throw-away one
Personalize a cocktail mix for a friend
Photograph yourself using a gift
Pledge to give non-bought gifts
Send a care package
Use a 2 for 1 offer to give the other item away
Happiness
Leave a cheery note somewhere unexpected
Make a list of mood boosters
Make someone laugh
Start a karma jar
Health
Buy a mustachey gift for Movember
Celebrate World Toilet Day
Click for autism therapy
Learn or teach CPR
Send a mosquito net
Sign up to an organ donation registry
Start a workplace exercise program
Surprise someone with a massage
Hunger
Eat at home for the Hunger Project
Give rice through trivia quizzes
Share your breakfast
Test your knowledge and feed a child
Information
Contribute to Wikipedia
Learn about the Guide to Giving's priority areas
Push for aid transparency
Share a report on the irresponsible super-rich
Share a slideshow
Share a useful piece of information
Spread the Overseas Aid Mythbuster
Watch and discuss an IRIN movie
Justice
Donate to the CIVICUS Crisis Response Fund
Help stop a dubious execution
Labor
Ask your boss to let employees work from home
Calculate your slavery footprint
Fight child slavery in the chocolate industry
Participate in the Underground Railroad
Provide items needed by trafficking victims
Pressure govt. on the migrant worker convention
Language
Correct someone's English - but nicely!
Fight gobbledygook with the Plain English campaign
Think about the words you use
Money
Demand ethical investments
Give change to charity
Microlend to a business in a developing country
Switch banks
Use a charity credit card
Movies
Make someone a movie mix
Museums
Give away the cost of a (free) museum ticket
Music
Customize an opera experience for a loved one
Download music for a charity
Ensure that your Itunes purchases benefit UNICEF
Pre-order "Kinshasa One Two"
Race
Relationships
Matchmake
Tell someone you love them
Reuse
Give away something you no longer need
Replace one disposable item
Take magazines to a waiting room
Science
Allow scientists to use your computing power
Ask for evidence
Sex
Buy an ethical sex toy
Buy Sir Richard's condoms
Perform a sex act without expecting reciprocation
Sexuality
Pressure PayPal re: homophobic groups' accounts
Send a support message to a non-homophobic church
Socializing
Donate in celebration to RNIB
Host a party for a charity
Social Networking
Donate a tweet a day to a charity
Join one of Plan's social networks
Sign up to a do-gooder social networking site
Sports
Buy a ticket to the Match against Poverty
Call for an Olympics human rights committee
Travel
Ask a travel company if it's signed up to The Code
Choose a charity challenge
Make your home available for couchsurfers
Save travel money by volunteering
Sign up to send ecards for Tourism Concern
Use a Green Passport as a travel guide
Volunteering
Ask your company to give time off for volunteering
Thank a volunteer
Volunteer at a World Heritage site
Volunteer your skills online
Waste
Give unwanted items to charity
Rent instead of buying
Water
Adopt a water conservation tip
Conserve rainwater
Shower with another person to save water
Ageing
Sponsor a grandparent
Animals
Adopt a gorilla
Be a friend to bees
Fight sale of animal-tested cosmetics in EU
Put food out for birds
Take old linens/towels to an animal shelter
Arts
Support an artistic project with Kickstarter
Take the time to appreciate a street performer
Books
Bring library books to a homebound person
Leave a book you love in a public place
Read a banned book
Show the MDG comic book to a kid
Business
Clean up after yourself in a store
Contact a company to say thank you, not complain
Help turn Volkswagen from the dark side
Use GoodGuide for more ethical shopping
Visit an independent business instead of a chain
Campaigning
Condemn the US funding cut to UNESCO
Share or post to the "We Are The 99%" site
Sign a petition
Children
Raise £2 for Save the Children with a click
Support the child soldiers treaty
Clothing
Buy "aftersocks" to help rebuild Canterbury, NZ
Pair up mismatched gloves
Communication
Ask "How are you" and really mean it
Compliment a stranger
Listen to someone
Send a fan letter to someone who isn't famous
Send an ecard
Thank a UN peacekeeper
Write to a political prisoner
Competitions
Enter the Rio+20 Global Youth Music Contest
Computing
Help publicize a great website
Help someone get online
Nag yourself into doing good
Try a new search engine
Cooking
Cook with weeds
Double up on lunch for a colleague
Get inspired by a vegan e-zine
Make a dish that reminds someone of home
Drinking
Buy Fair Trade liquor
Try to drink more ethically
Education
Donate items needed by a public school
Donate to the Scholar Rescue Fund
Give pencils by signing up for Camfed news
Exchange skills
Take action with a 10x10 partner
Thank an old teacher
Energy
Provide a solar light bulb to a Haitian family
Switch energy suppliers
Use short bursts of exercise to save on heating
Environment
Complain about excessive packaging
Copy an Earth Day pledge
Encourage the switch to paperless receipts
Plant a tree
Recycle one item you normally wouldn't
Food
Bring food to protesters or volunteers
Buy loose produce wherever you can
Buy out-of-date groceries
Cut one questionable item out of your diet
Implement a Love Food Hate Waste tip
Make healthy treats for a dieting friend
Pick some fruit
Post a recipe for ChildLine
Start a food sharing group
Treat someone to a meal
Games
Play online poker for International Medical Corps
Play WeTopia
Start a virtual tiger park
Gender
Become a member of ACWW
Shop to support female entrepreneurs
Take part in an International Women's Day event
Gifts
Exchange unwanted gifts
Give an edible mix
Give a reusable gift instead of a throw-away one
Personalize a cocktail mix for a friend
Photograph yourself using a gift
Pledge to give non-bought gifts
Send a care package
Use a 2 for 1 offer to give the other item away
Happiness
Leave a cheery note somewhere unexpected
Make a list of mood boosters
Make someone laugh
Start a karma jar
Health
Buy a mustachey gift for Movember
Celebrate World Toilet Day
Click for autism therapy
Learn or teach CPR
Send a mosquito net
Sign up to an organ donation registry
Start a workplace exercise program
Surprise someone with a massage
Hunger
Eat at home for the Hunger Project
Give rice through trivia quizzes
Share your breakfast
Test your knowledge and feed a child
Information
Contribute to Wikipedia
Learn about the Guide to Giving's priority areas
Push for aid transparency
Share a report on the irresponsible super-rich
Share a slideshow
Share a useful piece of information
Spread the Overseas Aid Mythbuster
Watch and discuss an IRIN movie
Justice
Donate to the CIVICUS Crisis Response Fund
Help stop a dubious execution
Labor
Ask your boss to let employees work from home
Calculate your slavery footprint
Fight child slavery in the chocolate industry
Participate in the Underground Railroad
Provide items needed by trafficking victims
Pressure govt. on the migrant worker convention
Language
Correct someone's English - but nicely!
Fight gobbledygook with the Plain English campaign
Think about the words you use
Money
Demand ethical investments
Give change to charity
Microlend to a business in a developing country
Switch banks
Use a charity credit card
Movies
Make someone a movie mix
Museums
Give away the cost of a (free) museum ticket
Music
Customize an opera experience for a loved one
Download music for a charity
Ensure that your Itunes purchases benefit UNICEF
Pre-order "Kinshasa One Two"
Race
Relationships
Matchmake
Tell someone you love them
Reuse
Give away something you no longer need
Replace one disposable item
Take magazines to a waiting room
Science
Allow scientists to use your computing power
Ask for evidence
Sex
Buy an ethical sex toy
Buy Sir Richard's condoms
Perform a sex act without expecting reciprocation
Sexuality
Pressure PayPal re: homophobic groups' accounts
Send a support message to a non-homophobic church
Socializing
Donate in celebration to RNIB
Host a party for a charity
Social Networking
Donate a tweet a day to a charity
Join one of Plan's social networks
Sign up to a do-gooder social networking site
Sports
Buy a ticket to the Match against Poverty
Call for an Olympics human rights committee
Travel
Ask a travel company if it's signed up to The Code
Choose a charity challenge
Make your home available for couchsurfers
Save travel money by volunteering
Sign up to send ecards for Tourism Concern
Use a Green Passport as a travel guide
Volunteering
Ask your company to give time off for volunteering
Thank a volunteer
Volunteer at a World Heritage site
Volunteer your skills online
Waste
Give unwanted items to charity
Rent instead of buying
Water
Adopt a water conservation tip
Conserve rainwater
Shower with another person to save water