You'll be able to buy a Ratchet & Clank Collection for PlayStation 3 later this year. It collects the first three games in the series, all wonderful, all from the PS2.
It omits the fourth PS2 Ratchet, the armored-hero multilplayer-centric, more badass Deadlocked. We would like to commend Sony and Ratchet creators Insomniac for their good taste in Ratchet & Clanks. More details at the PlayStation Blog.