I hv been quite busy lately and was completely aloof from gaming. GTA was my best games of all no matter how much resources it used to HOG. The last one I played was Episodes from Liberty City.
That still remains the latest release from Rockstar. There's no news on any upcoming GTA titles, although I'm 100% sure there will be more from the stable.
In the meanwhile, you might want to try Mafia 2 if you haven't already done so. It's the same gameplay, better story IMO. Another one is L.A.Noire. It's already out on the consloes, will be out on PC in November.
Mafia 2 is my all time favorite game. It is to much better then GTA and you should also check saints row 2, it is also nice game.
Mafia 2 is similar to the GTA series, but it lacks free roaming a little bit. As said, GTA's episodes from liberty city is the latest one yet. Rumors are there about a newly releasing GTA V, but it's yet to be confirmed.