There is a left 4 dead 2 mod that you can run split screen. It's great, but can't remember what it's called or how to do it!?! A quick google search will show you the way. Also street fighter 4 is ok.
But as someone said, Lego games are great too. Got my mrs into them for a while. But we argued a bit because she can't jump onto ledges and I got frustrated. She would then get all menstrual when I said "let me do it" after her 20th attempt. Comical really. And they always seem to get carried away collecting the coins Rather than help solve the puzzles. It's like trying to teach a dog tricks...
Haha I have exactly the same issue! Left 4dead mod sounds a good idea as she agreed to try l4d so if we can split screen that'll be awesome although its an fps so may struggle.