Dead Rising 2
Its a big sandbox game with some story but very fun for to people. Keep in mind this has no lan
Saints row 2
Best coop game every.
If you don't mind an mmo experience then nexon has got a lot of free mmo such as mabinogi , maple story , and vindictus.
Play it in one with two joypads you and your friend
Bomberman would be fun !
Classic but awesome game
Dead rising and saints would be good you dont need any experience to have fun in either of these games. then again i felt the exact same way about borderlands.
If your looking for something like diablo 2 you can always try titans quest. huge diablo clone. left 4 dead really isnt that fun with just 2 people. you would probably finish all of it in about 4-5 hours on normal.