[deanfranks]

If you want to learn assembler to analyze malware, learning x86 assembler under linux or windows is where you should start. If you really want to start with a microcontroller, the AVR is a good place. You can use one of the Atmel XPlain boards or an Arduino with the Atmel Studio. I would recommend getting an AVR Dragon JTAG interface, being able to debug at the hardware level is invaluable when you are learning or doing "real" development in assembler.

Note that a good portion of the learning curve for AVR or other microcontroller assembler is learning the hardware environment and learning about interrupts, execution environment setup, etc etc. None of this is particularly useful for malware analysis on x86 hardware.

If you are going to analyse malware under Android/etc then ARM is not such a bad idea. The PI or the BeagleBone are excellent platforms for getting started. Be aware that ARM assembler is a bit of a beast and is probably not a good first architecture to learn.