List them out for me, please- I'm looking for more to try.
Loved starscape by moonpod games. I played that fanatically for like a year. Everyday Shooter was fun but I didn't stick with it once I made it through the levels.
And minecraft of course..
Torchlight (diablo inspired RPG), Hard Reset (Fast paced challenging FPS), Minecraft like others have said.
Also if you are wanting to get cheap indie games in bulk I highly recommend Indie Humble Bundle's website and Indie Royale. Can get some good gems for super cheap when packages are rolled out. I can say I have done business with both sites multiple times and have had no problems dealing with them.
minecraft, Cobalt, Super Meat Boy, VVVVVV, Cogs, Jamestown, Nightsky, BIT.TRIP RUNNER, Terraria, Cave Story+, Dwarf Fortress,Super Smash Land, Kerbal Space Program, and Gratuitous Space Battles can be pretty fun.
Those are all the ones I have played that I think are really fun but my Favs are probably,
Cobalt, Minecraft, Super Meat Boy, Cave Story+, and Cogs
when I am in the mood for some puzzles.
I'm a big fan of Frictional Games' survival horror games, Penumbra (Overture and Black Plague / Requiem) and Amnesia (The Dark Descent and the upcoming A Machine For Pigs). Of course, I also love Minecraft, but that game has become so popular that I'd almost hesitate to call it an indie game (though of course Mojang is in fact an independent developer).
The Binding of Isaac - Plain and simple, has HUGE replay value. There aren't many games I play over, and over again such as Binding of Isaac. It's very unique and fun to unlock all the new stuff and see how Isaac changes in each play through (as they are all unique).
Minecraft - This is definitely a given.
Audiosurf - Fun to play here and there.
Terraria - I have not played this *yet*, but the second it's on sale I'm getting it. It looks like tonnes of fun.
Super Meat Boy - Well, it may drive you insane playing it! But it's a blast.