This one managed to slip by me. I'm not sure on the exact release date, but looking at digg.com makes it look like it was released only a couple of days ago. There are seperate downloads for Visual Studio 2005 Team Suite (includes SP1 updates for Standard, Professional, and Team Editions of Visual Studio 2005), Visual Studio 2005 Team Foundation Server, and Visual Studio 2005 Express Editions. The version for Windows Vista (beta) is apparently coming soon.
There are a lot of important fixes in this service pack, especially for anyone working with Team Suite to do load testing work.
Link: Visual Studio 2005 Service Pack 1 (SP1)
Link: ScottGu's blog: Visual Studio 2005 Service Pack 1 (SP1) Released
Link: Digg.com: Visual Studio 2005 Service Pack 1 (SP1) Released