Tried demos for eXtinction and Caster, but I dont think I'll buy either.
I've played the following before: Flatspace, LArva Mortus, Spectomancer, Age of Booty, Gish, Starscape, and Mr Robot. I might redownload the Larva Mortus demo because I'm sort of blanking on what it was like.
I do enjoy the Spectromancer demo. Its a card game by one of the co-creators of Magic: The Gathering. No lands, you just gain 1 mana of each color every turn. You get a random selection of 4 cards in each mana type that you then use to battle it out. It works quite well. Only thing is I don't know anyone else that would buy it so I'd be stuck playing AI. Still, not a bad option.
Same sort of problem with Age of Booty. Don't know anyone else with the PC version. That and the 5 activations thing still rubs me the wrong way, even on a $10 title.
So yeah, still trying to decide. Hmmm...I wonder if I can use it to preorder Elemental and get into the beta. *ANSWER* Yes you can. The download + retail box would take $10 off so basically its free shipping on the deal.