These folks allow you to use a version of Yahoo! search where 50% of ad revenue goes to a charity of your choice:
On your first visit, you can choose the charity (Wikimedia is among those supported). You can also review how much money has been raised so far (apparently $3 in January). Pretty cool, IMHO. I've set it as my default search and will see if it makes a difference. I _do_ search a lot. :-)
Now let's hope Yahoo! doesn't suck too much compared to Google .. ;-)