Best Multiplayer Games

My girlfriend has finally warmed up to playing my PS2 with me. We love playing Burnout Revenge. However, most of the games that I buy are single player (RE4, GOW, Hitman, Some sports games).

When I play games with my guy friends, I usually just play a sports game. But are there any other good 2 player games that I can play together with my girl? Please let me know. Thanks!

Depends what she likes.

 I've been playing quite a bit of Batlefront II with my girlfriend since we both love Star Wars and shooters.

Marvel: Ultimate Alliance, Onimusha: Dawn of Dreams, Ratchet: Deadlocked, Destroy All Humans, Def Jam: Fight For NY, Mortal Kombat: Shaolin Monks, The Warriors and Lego Star Wars I & II are various games we've played lately off the top of my head that we've enjoyed.

 My girlfriend likes playing games (moreso than me actually) and loves violence. I've heard most guys have issues with their girlfriends having extreme aversions to anything of the sort, so it truly depends on what she likes. There's also plenty of other ones. Most are either shooters or beat'em ups and the like.

You can't go wrong with Lego Star Wars though. 

burnout 2 was more entertaining than new ones for me

lego star wars series are nice

x-men legends 1,2, marvel ultimate alliance are like rpg beat-em up 

Well, if she doesn't mind running around a battle field, slaying hundreds of enemies, Samurai Warriors 2 should be a good fit.  It's the best out of all of the DW and SW games and it has a lot of great characters.

Ratchet: Deadlocked

Great Co-op and online multi player