Reccomend a CPU emulator to teach assembly program

I think many microcontroller manufactures offer free IDE+assembler+debugger+emulator for their microcontrollers. I have programmed Atmel 8bit AVR series a little bit and tools were very usable.

From botton of the page: "AVR Studio 4.12"
http://www.atmel.com/dyn/products/tools.asp?family_id=607#soft

IDE: