Ursine Paw released a very slick game called Run In Crowd a bit back that has an interesting take on multiplayer. It is one of those run and jump games where you run and tap to jump over obstacles. The coolest part is that you can run against other players to compete. The game is totally free but you can purchase outfits or customized characters for $0.99. The levels are dynamically generated and you can view the top 15 high scorers here.
kudos to Jon @PocketBerry for spotting the game!