International Women's Day is March 9, giving you plenty of time to make your estrogen-centric preparations. The theme for this year is "Connecting girls, inspiring futures". Whether you want to teach, learn, advocate or just fill up your Friday, a list of events by country is available at http://www.internationalwomensday.com/events.asp. The website is rather cluttered and corporate-branded, but is still a useful resource.
Effort involved: it depends on what kind of event you want to participate in (or even host). Or just send a snarky ecard or email vaguely related to X-chromosomeyness.
If someone you know is an opera fan, there are several reasons you should immediately buy one of these "operagrams":
1) The singer's name is Baroness Tamara von Stein zu Leitershofen, which ranks up there with Florian Henckel von Donnersmarck in the roster of all-time great Germanic names.
2) Distance is no object. If you're in London the singing can happen in person, but for everyone else the operagram can be delivered online or over the phone.
3) The proceeds go to a children's NGO in Lesotho.
4) It's a different kind of Valentine's Day gift, which also happens to be affordable.
If you're convinced, mosey on over to www.operalapdiva.com/charity.
Effort involved: buying and customizing an intangible gift. How hard can that be?
I can't say it any better than the original article, so I'm just going to direct you to the original article: http://lifehacker.com/5877393/how-to-book-a-1700-vacation-for-700-by-volunteering. Any accusations of laziness on my part are not unreasonable.
Effort involved: it depends on the kind of volunteer tourism you do, but there most likely will be some physical exertion (the physical kind is less likely but still possible). But what you expend in sweat is compensated for by what you save in money, making this a good deal if you're time-rich but cash-poor.
Image from: http://now-here-this.timeout.com/2011/12/09/nick-waplington%e2%80%99s-holy-landscapes/