In the latest Atmel Applications Journal (registration required), they have a couple of articles for setting up AVR-GCC under Linux. Unfortunately, when I tried to follow the instructions, some of the links weren't working.
However, while googling around for alternative download sites, I found Rod Moffitt's site, here.
He mirrors all the packages he used, and also has a build script that drives the whole process, so you don't have to worry about separate steps for compilation of each tool.
It also uses GCC 3.4.3, which is more recent than the version linked in the AAJ article (which was 3.3.1).
I haven't compiled anything with it yet, but this site hasn't been mentioned here before (that I can see) so I thought I'd share it...