Alex,

You can find some tools for FREE: assemblers, simulators and even tiny compilers. This tools can be useful for the first steps in the 8051 family. However, when involved in the development of serious applications, you need to spend some money.

Look for available tools in www.8052.com

BTW, have a look to UVI51 (is free) in
www.dte.uvigo.es

I think is a good tool for beginners, specially designed for students. Of course, my opinion is a little biased because I am the author :).

Regards,

Alfredo del Rio.