All-time Best Indie Games (jayisgames.com)

I recommend Cave Story+, Bastion, Terraria, Spelunky, Legend of Grimrock, and Machinarium from that list. I would also add Dungeons of Dredmor and La Mulana. Merry Christmas.

I can't believe Braid isn't on that list. SUCH a great game. Also, Portal is a must-play if you haven't already.