We've found a job listing from Insomniac Games which reveals that the Ratchet & Clank and Resistance developers are working on their next title, and as expected, it's a PlayStation 3 exclusive.
The job listing is for an FX Artist, and states that "Insomniac Games is looking for an artist to create effects to work and assist in gameplay, environment, and the cinematics of the game."
The developers latest title, Ratchet & Clank Future: A Crack In Time was only released in November last year, so it's unlikely to be the next instalment of the R&C series. A few months ago though, a picture of a billboard with the logo of Resistance 3 sprung up on the internet (top of page), so we expect this is the next title in the FPS series.
http://connectedconsoles.com/ps3-Insomniac-working-on-next-PS3-Exclusive.cfm