Second Orcs must die- fantastic game.
Dungeon defenders.
world of goo
Rock of ages is pretty awesome too imo
You basically try to kill each other by knocking down their base door and running him over with a huge rock. You get gold which you use for defending your gate. Using towers/catapults/elephants to slow down your opponents. you get gold by smashing defence structures. The rock itself can be upgraded too. Has a singleplayer and multiplayer component.
I would include mobile games. There's a bunch of indie games on iPad that have been amazing for me. Hundreds is the one I'm stuck with atm. But also the following:
Badlands
Machinarium
Kingdom Rush HD
Stickets
Beat Sneak Bandit
The Room
Superbrothers: Swords and Sorcery
Lost Winds
Swordigio
Horn
Lili
Year Walk
Magicka
Ridiculous Fishing
Little Inferno