Their SPU Instruction Cheat Sheet has a permanent home on my desktop.
The Insomniac Tech (R&D) Page is a great source for PS3/performance/game-programming related information. Even if you happen to not like their games or subscribe to their approach to SPU programming (by choice or otherwise), they've got a lot of resources related to different aspects of engine and game development. And since they are a game studio all the information is very "practical". I applaud their openness and willing to share information online, at GDC, etc.