Me and my girlfriend actually just played It Takes Two. Absolutely phenomenal game. Really fun to play and a bit emotional for her due to family problems. But an amazing game. Be ready to really learn how to play well together to get through some of the bosses. It took us about 2 weeks off and on about 1-1.5 hour play sessions, but it was so worth it.
A fun fighting game that gets away from Smash Bros clones is Stick Fight. Even good for more than 2 people!