Humble Indie Bundle, for example, has an option to donate to charity when you buy. Now we have another multitasker on our hands.
The nine games in the next Green Light Bundle, launching on February 1, are the following: haunting sim Paranormal, tower-defense game Beware Planet Earth!, tile-dragging puzzler Hairy Tales, casual dungeon crawler Dwarf Quest, spearfishing sim Depth Hunter, 8-bit platformer Potatoman Seeks the Troof, beat-em-up Megabyte Punch, platformer Gear Jack, space strategy game Aeon Command. All of these games, except for Depth Hunter and Beware Planet Earth!, are on Mac as well as PC.
If you buy, don't forget to vote for these games on Steam. It's your civic duty, after all.