AVR-Chat

Compiler-goodness debates!

My experiences:
GCC - free. IDEs are from other cottage industry or freeware types. Hard to
use. Does NOT support tiny memory model for small AVR chips. Support is
limited to forum on AvrFreaks and often you get an answer from an arrogant
compiler guru who hates corresponding with the little people. But it's free.
Students love it. I'd never use it for a professional endeavor where there
are contractual issues of project completion and acceptance/support long
term. But it's free. I've used it a lot. 

Codevision (CV). US$150 or so as I recall. Free demo.  Code density for my
projects was great. Supports tiny memory model for 2313 and the others with
256 bytes of memory (8 bit RAM pointers) and this has a big benefit in code
size. Great support.

I've not used any of the others.