XCOM would be a great choice. I left it unfinished because I was too lazy to transfer my save file from my laptop to my desktop when I changed computers and I've been thinking about replaying it. Although, I'm about to go on vacation for two weeks so I won't be able to play much at all until September.

I'd suggest that the game be no more than $20. I can see an exception for XCOM, as many people probably already have it.

Game suggestions:
Dishonored (it would be interesting, since the game changes based on how you play)
Final Fantasy VI
Portal 2
Valkyria Chronicles
Zombi?
OR wait until something really good comes up for sale on PC

Edit:  by the way, Greenman has a 23% off deal right now, making it cheaper on most games than Steam.

Now that you mention it (XCOM aside, since a lot of people seems up for it), why not Deus Ex: Human Revolution? That game is a joy to play/replay, and it's available in a wide range of platforms.

I was going to suggest that, too, but I was afraid people would get mad because too many FPS.  It's a great game.

$15.40 on Greenman with voucher.

Wish I owned the Director's Cut.

Your chance to reedem that, and plus having fun with your VGC mates!

I think I'm going to propose those two games for the final version.

I wanna join. But I don't own any XCOM: Enemy Unknown or Deus Ex: Human Revolution capable systems.

I'd say Deus Ex is very cheap nowadays for ps3/360, if you happen to own any of those.

I would prefer it to X-COM, I think.  My problem with X-COM, besides the price, is that there is very little story or character growth, thus not all that much to talk about.  That's what kept me from suggesting Torchlight 2, which is also a great game.  I already have X-COM, though, so I have no problem if it's chosen.

My top choices would be (in no particular order)

Deus Ex: HR
Valkyria Chronicles
Dishonored

I have a broken 360 and a PS3 from my girlfriend who's too lazy to get it back. I'll check if she has Deus Ex. Maybe we should play Metal Gear Solid. You know, in celebreation of The Phantom Pain's release?

Just played a hour (3 missions total) of XCOM and it is pretty fun (even with the hand holding on the first two missions). I have Deus Ex on Wii U that I haven't even touched yet.  I suppose I can focus on beating both.