God, I could probably spend a week typing up all of my favourites! But I feel I should single out Toejam and Earl for being probably one of the most unique 2-player experiences that there was (and is). There's nothing quite like the sheer terror-inducing moment of your buddy opening a random present to find out it's actually rocket skates and not the fudge sundae you were hoping for. Or the feeling garnered from turning someone down after they ask you to share a life when they're out and you have one to spare.Actually, you can tie a feeling to that - a dull pain in the arm care of the person using the controller next to you!
Bubble Bobble.