After completing the epic God of War III , Sony Santa Monica wouldn't say anything concrete about the future, but they have said they don't want their award-winning franchise to become an annual occurrence.
However, are we already seeing evidence of a new God of War project? All the rumors and speculation you've heard likely started with new job listings at Sony Santa Monica; those jobs can be found at the Playstation Careers website . You can also see a screen capture of several of those jobs at GamerXChange . It seems they're hiring for the following positions:
Of course, that doesn't necessarily mean the new employees will be working on a new GoW title, but Sony Santa Monica is certainly best known for one of gaming's series. We have no idea if Kratos will be back and in truth, considering the ending of GoWIII, there's no knowing where the team will go for the fourth installment.
It seems HipHopGamer may have some inside info as well; GoWIV will feature 3D, co-op, and "better visuals" (as if that's any huge shock). But right now, we know nothing and we have to admit that. Perhaps we'll get a huge unveiling at E3.