While Ratchet & Clank: Quest For Booty has been long rumored and has shown up on several PSN release lists - it's never been officially announced. Over the weekend some actual evidence showed up - in Spanish!

This logo, which translates to "Ratchet & Clank: In Search for Treasure", was apparently found on the Sony Computer Entertainment Spain website.

According to some extra info, it does appear to be a PlayStation Network game, and not downloadable content for R&C: Tools Of Destruction, as well as including some sort of online mode.

Source: NeoGAF - Ratchet & Clank: En Busca del Tesoro ? (PSN), Thanks to Endless!