Well, the best one I know of is this one:

http://www.amazon.com/exec/obid...66-7093856

The guy who wrote it is my professor and I can tell you that it is written from the perspective as you have never written a program in your life. Although it is not geared toward the 8051, by learning the 8086 instruction set you will be able to learn the 8051's in about a week. Deffinately the best book I have ever purchased involving Assembly instruction as well as interface design.

Have a good one!
Phil