20. Gauntlet: Dark Legacy
PS2, 2000
This is perhaps my favourite co-op game ever, although you really need four people (and preferrably silly gamer types with a few drinks and an evening to waste) to allow it to really shine. It's a simple game but that is what makes it great - it does enough to occupy people and do their best to work together to some extent, it's cheesiness allows everyone to laugh it up and not take anything seriously but it's not so hard that you have to actually be focused in order to play it - you can talk about whatever the hell you want while you game.
When Matt and Shauna next visit this will be high on the agenda as far as I'm concerned.Also, this is probably one of only 2-3 games (well, game series, but this game in particular for Gauntlet's series) that I will ever actually still swith my PS2 on for.