Right now, I'm playing World of Warcraft (still, Jesus Christ), Empire: Total War, Fallout 3, LittleBigPlanet, and Fight Night Round 4. My girlfriend owes me a birthday gift, and she asked me which game should I get. I only play games that have long single player replay value (which rules you out, Uncharted 2). World of Warcraft is an exception, because that isn't a game. That's a drug.

Anyway, can anyone suggest a game for me? I'm having trouble deciding. I only game on PC and PS3. 

if you havent already beaten oblivion to death i recommend it. there arent too many games that have long replay value right now. if you want another mmo that you may never reach max level and do everything i recommend trickster.

Demon's Souls and Disgaea 3 come to mind.

final fantasy tactics :D (ps1) but if it must be current gen demons souls looks like that has lots of gameplay to be squeezed from it.

demon's souls is an rpg yes? not sure why that would have a lot of replay value.

Pretty much every Fighting-genre game lives and dies by its replay value.

Oblivion, I have played it here and there for a couple of years I guess and still haven't beaten it. There is so much crap to do it's not funny.

because it's about grinding, playing the game again and again at higher levels, and cooperative and competitive multiplayer.  It has a lot of replay value if you end up enjoying it.

Viva Pinata!!!!!

or Batman. I have played through the campaign three times

There are several posters on this website who want you to buy Demon's Souls no matter what Bugrimmar. 

Torillian is one of them.  You should generally ignore anything he says about the game as it's heavily biased.