You definitely want to get tavrasm here, if you have a Mac.

-And if you don't have it already, get AVRMacPack from obdev.at
This site will be used for dumping any leftovers from my AVR fun.
-Well... Maybe a little more. If it has a chance of being useful to anyone, I'll probably put it here.
-Sorry, no fancy pop-smart blog, forum or the like. I just don't like bloat.

I'll most likely make a beginners guide to getting started with AVR on a Mac. Until then, have a look at this page.

You might also be interested in the GAL assembler: gal.bruger.mine.nu