The original Mafia was just re-released through GOG.com today. This is apparently a part of the 15th anniversary of the franchise. Honestly, this is the first I've even heard that it's the 15th anniversary of the franchise, so I have no idea if there was anything else or if anything else is still planned.
Mafia is just $14.99 (USD) through GOG.com. It should be noted here that the licensed tracks that were a part of the game's original release are not include in this version...