Fighting Force??

(Sorry guys.

)
Nothing beats the likes of Double Dragon, Final Fight, and Streets Of Rage. Sengoku 3 rocks too. Really if you want co-op, get yourself MAME and some PC-enabled pads or sticks and go to town...there's tons of games out there. And if you want more Contra-style action, don't forget about Metal Slug 1-6!
Best co-op experience I've had in a recent game was Crackdown. Before that was probably both Champions of Norrath games on the PS2.