fun co-op game to play with girlfriend

LEGO games, http://store.steampowered.com/search/?snr=1_4_4__12&term=lego

Castle Crashers!
Torchlight 2
Sanctum Series...

Just use the Co-op tag in steam...

Battleblock Theatre.

I know of a co-op game. But it's not on steam... and requires a flat surface.. so... ummm... yeah..

Rayman Origins and Legends, or Super mario bross 3D World. not the other super mario bros Wii or WiiU because those would make you break up

Magicka?

spelunky, rush bro., giana sisters..
of course, it could be more interested when you and your bear sit besides :))

or you could try nintendo emulator with Bomber series :))

Left 4 Dead 2

Portal 2 co-op is a really special and unique experience.

How has Portal 2 not been mentioned yet? One of the best for co-op experiences.

EDIT: 37 seconds late... you win Tinepou.

I liked the game Ibb and Obb, it was all co-op and rather fun.

Oo cute game....to play with your gf.... <____< If my bf tried to find a "cute" game for us to co-op, he'd get his ass kicked.... <___< We just got done with a round of Dead Island, second one of the day, both about 2 hours or so. Been enjoying that.

A fun one though, is Monaco, and you can make your own maps and quests on that. I loved playing that. TL2 with mods. Saints Row 3rd is amusing. Most the Lego games are amusing and fun.

I don't tend to apply "really good" and "cute" in the same sentence when it comes to video games. However, Magicka is an amusing little timesink that those phrases could apply to, though YMMV.

Also Chivalry, Mount&Blade:Warband, and Space Hulk, obviously.