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.

http://www.cl.cam.ac.uk/freshers/raspberrypi/tutorials/os/

I took an interest in malware analysis last autumn and cant recommend the book Practical Malware Analysis enough. It introduces the subject to a beginner including the wide variety of skills required and tools used. One of the best things about the book is the malware samples supplied for analysis at the end of each chapter and then the detailed walk-throughs of how it should have been done.

The book focusses on windows malware and thus discusses x86 assembly, both an introduction to and identifying the constructs of higher level languages on dissassembly.

I immediately looked to supplement the information on assembly however. First with the Linux Assembly and Windows assembly "megaprimers" on securitytube.net, then with the Intermediate Intel x86 series of video lectures on opensecuritytraining.info. The quality of the latter was very good, so much so that I may go back and watch the introductory x86 lectures as well. I'm not usually a fan of video tutorials, but I thought the format suited the topic quite well.

I've stopped looking into malware analysis for now due to work, part time college and side projects that will hopefully lead to better work in the short term. I do look forward to picking it up again in the future though, its really quite fascinating.