Incidentally, "AVR" == "Arduino", so if you want a HEX file to execute you can have the Arduino toolkit drive the GCC cross-compiler for you, while you sit back sipping mojitos. Download the Arduino toolkit, open up the "Blink" demo, and press "Verify / Compile". Watch the little message window as your code compiles: Near the end of the process it will cough up a line like this:

/var/folders/4x/cwc9yvnx071_9whsft75cjvc0000gn/T/build8742301187783484704.tmp/Blink.cpp.hex

That file seems like it would be a fun thing to explore.