Thanks for all the suggestions! :)
I checked out Torchlight, definitely will get this game, it looks awesome. :D Torchlight 2 is going to be massive with the coop multiplayer. :D
To turn around things, we'll start with storyless game. Sorry about that. So, a session of FlatOut is on tonight. I was surprised, but she likes the game. :)
I'll check out the games that were suggested here tomorrow.
By the way, any other GOGs having a coop mode? :)

Especially when it's on sale right now on Steam. I'm getting three friends together so we can buy the four pack at around $8 a person.

I know that the Neverwinter Nights games mentioned before are totally designed for group play so co-op should be possible. Too bad Crackdown is console only because that is a blast on the 360 in co-op.
Hmm, oldies like System Shock 2 and X-Wing vs. Tie Fighter are a blast as well, or if you don't mind a little light stuff hot seat Peggle is good too. :)
My wife and I have played various puzzle type adventures via over the shoulder co-op. and that is a blast for us, so games like Myst or Phantasmagoria and the like where you bounce ideas off each other might work too.
Oh, and Descent 3 had good co-op too and is available here. :)

"Posted: 4 hours ago..."
Damn you. Damn you to hell for not only making me buy another game, but on Steam to boot ;P.

Die by the Sword co-op is hilarious. I played it with my brothers, and we were laughing all the way.
Also, just to repeat again for emphasis: Din's Curse :)

Your quoting a Diablo 2 fanboy, thems fighting words...

We checked it out, and don't like the graphics style. On both games. So we're kind of after a cartoon-like style, something similar to Torchlight.
By the way, Peggle Nights duel turned out to be quite fun. :)