A bit out dated, yes.... but its pretty fucking fun! SA-MP is a mod for GTA: San Andreas for PC which allows you to play online. I am currently playing with 130 people on:

HostName: PartyServer v5 [0.3C] [KFCGang.net]

Anyone care to join? It's pretty sweet, you can choose different "gangs" and there are real turf wars, which you can start and join, random events that pop up and you can type /enter to join (hovercraft races, ambulance races, etc) there are a few mods like some helicopters have giant magnets you can pick up cars with (if you're good ) It's kinda like CS:S, every server has their own mods that are different from another. I play this server mainly because there are so many people online at once.

[VIDEO]http://www.youtube.com/watch?v=kK_-sVtmkpA]GTA:SA Multiplayer SAMP Party Server - YouTube[/VIDEO]