I think I have used enough of the AVR series by atmel to say that I understand how to use it. I know somethings about how it actually works, but I would like to know more. Are there any good resources which describe the architecture of Atmega or RISC architecture in general? I know the datasheet has all this (and I really looooovvee the datasheet, its kinda my bible) but I need something little more simple than that. Any help?
Learn AVR assembly, it's the best practical way to learn about the architecture.
Check out the white papers in the Other Docs section of Atmel's website: http://www.atmel.com/dyn/products/other_docs.asp?family_id=607#White_Paper .
A long time ago I read the one called The AVR Microcontroller and C Compiler Co-Design which explains why they think the AVR instruction set is well-suited for the C language. Some of the other documents there explain the AVR architecture or a series of chips in general.