The last Katamari game to come out will be Me And My Katamari, for the PlayStation Portable. Though given that this game was created without the input of Keita Takahashi, the designer of the Katamari concept, it's not inconceivable that Namco (who, presumably, own the characters and trademarks) could bring out more sequels if doing so would be profitable; they're already giving the characters cameos in other, more traditional, games.
Takahashi is apparently working on a new concept, unrelated to the Katamari games. It'll be interesting to see what he comes up with.
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