Namco's official Katamari Damacy site has a cute little low-tech online version of the game -- click on "Presents" and "Game" to play.
Snowball, an ad for Travelers, has clearly been influenced a wee bit by Katamari Damacy.
At E3 in 2005, there was a katamari that conventiongoers were encouraged to stick random items onto. Thoughtful of them to prop it on metal poles so it didn't get loose and go on a rampage.
At Making Toys, a toy-design blog, there's an innovative prototype for a katamari racer game: remote-controlled cars driven by cousin dolls and outfitted with velcro katamaris to pick up objects. Cute!
Don't forget the celebrated soundtrack. I was introduced to the music by an eager fan even before I ever glimpsed the game...