IGN: Rapping with Parappa's Maker
In-depth report on the promotional Um Jammer Lammy gig held by Sony, including the press conference with Masaya Matsuura and Rodney Greenblat.

Whimsyload
Artwork by game artist Rodney Alan Greenblat

Neoseeker's Um Jammer Lammy Resources
Offers FAQs, screenshots, a discussion board, and links to reviews.

Anime Lyrics: Um Jammer Lammy lyrics
Lyrics from the "Make it Sweet!" album, most of which come from the game itself.

Elfwood FanQuarter: fan art by Sarah Guilbeaux
Um Jammer Lammy fan art drawn by Sarah Guilbeaux. Mostly pictures of Teriyaki Ono, with a few of Lammy, Rammy and Parappa.

Pink Milk and Munchies BBS
An English language bulletin board for discussing Um Jammer Lammy. Includes fan art and fan stories.

Level 80
Contains various hints for the game.

Um Jammer Lammy
Official Sony of America page. Flash-based site with character biographies, screenshots and an overview of how the game works.