Imagecraft has released the demo version of their ICCV8 C compiler tool for Atmel AVR microcontrollers. The demo version is unlimited for 45 days, and code limited thereafter to 64K, non-commercial use only.
One helpful feature in this IDE is the App Builder. This tool allows for quick setup of peripherals on a number of AVR devices, such as timers, SPI, I/O pins, interrupts, etc.
Check out the description of App Builder from the Atmel Applications Journal. (While written for ICCV6, this description still applies.)