Be Excellent To Each Other

http://www.wolfire.com/humble

Aquaria,
beautiful 2D underwater metroid.

Gish,
Puzzle Platformer

World of Goo
You must know this

Lugaru
?

Penumbra Overture
?

Absolutely no reason to not get this.

I gave $20, given that I already have some of them, but want to give money to the EFF.

Lugaru
Rabbit based punch em up. 3rd person fighting game with a pretty great combat engine. A bit amateur by todays standards, but really fun. I've not played the "HD" version, but I think it just includes a bunch of fan enhancements to pretty it up.

Penumbra Overture
A brilliant step in the right direction for adventure gaming. It's a lot like a horror point and click adventure, but from first person perspective, and with a brilliant physics/interaction interface. Creepy as hell too.

Edit: I'd be all over this if I didn't own them all already.

I like that when you put in $0 you get a picture of a down-n-out indie developer