best ad-hoc multiplayer game

what do you think is the best ad-hoc multiplayer game? i'm looking for one that i could play with my brother on trips and such... so a good two player ad-hoc one.

Lord of Arcana that's coming out this Tuesday looks pretty sick. It's basically an action RPG where you try to take out huge monster and whatnot. Try the demo, I think you can test out the ad-hoc multiplayer with it.

Monster Hunter Freedom Unite