I think the Codevision compiler is great. Here are some of my favorite features:
- Demo version for free, inexpensive to buy the full version.
- The Codewizard saves time getting hardware set up-- no more datasheet on lap trying to figure out registers!
- The UART on chips that have one is mapped to standard i/o, so printf sends serial data out.
- Floating point and full c math libraries-- try that in assembly language!
You also need the atmel AVR Studio (free download) to debug your software, either in the system with a JTAG programmer or by simulating it on your PC.
