Get at least 3 games for 5 dollars. That's the minimum donation amount. Though you certainly allowed to pick as many more from the list of games as you like.
The amount of your donation increases by $1.67 for each additional game you decide to pick with your donation.
That's a minimum of $5 for 3 all the way up to a minimum of $21.67 for 13 games. Though if you want to help out this great charity then by all means donate more. There is no limit but there are minimums set for however many games you pick.
These games include some oldies and some indies: FTL, Darwini, Driftmoon , and Botanicula (check out my review of this game here) are some of the 13 game options.
If you want to learn more about this charity:
The sale only has about 16 hours hours left as of writing this post.
Get them while their cheap! Click here to get to the sale if you haven't clicked the first link already.