Im new to micros and assembly too. I've looked at several different sources on the internet. I think the 8051 tutorial here is the best place to start(Chap 1-5 first). If your like me, you will have to read it over several times and you have to know binary and hex numbers.

I found the Simple Microprocessor Course at hkrmicro.com to be good for getting started with assembler(Chap 1-7).

After you studied this, then you probably want to go to the Philip fam docs that listed in erik malund's post. That' the way I've been studying and Im learning fairly well. Better than the book I paid $75.00 for and sent back!