StreetWars.

Recently, StreetWars gained a lot of media attention (it was also featured in one of the CSI series):

You can hunt your target down any way you see fit; you can pose as a delivery person and jack them when they open the door, disguise yourself and take them out on the street, etc.

If you are successful in your assassination attempt, the person you killed will give you their envelope and the person they were supposed to kill becomes your new target. This continues until you work yourself through all the players and retrieve the envelope with your (or your team's) picture(s) and name(s). Then you win. Cash…but first live in fear.

Link | LA Times Article (Thanks Reid!)