I'm not sure how true this is, but so far this site I visit
(the sister of the Xbox 360 Achievement Guides) claims to have news of GTA 4. Hmm, about time? I'd say so.
I've seen tons of games hitting the Trophies list so apparently me investing money and time into Stardust HD worked, since I know sales sky rocketed when Trophies were finally released. I don't even mind replaying GTA 4 again. If only Solid Snake could get his butt a trophy, I'd be set.
Other games 'rumored' to be getting Trophies soon are Dead Space, Eye of Judgement, Quantom Solace, and some others like Blitz II.