For a "REALLY GOOD" disassembler you should look into the IDA package. IDA == Interactive DisAssembler. You can go to web site <www.datarescue.com>. This package can disassemble almost any processor including the 8051/8052. It is truly interactive and with a bit of time you can interactively make a disassembly listing look just like source code with symbols, line comments, block comments, and data tables.

Once I got this I never needed another disassembler and I have used it more than once to re-create lost source code from the object read out of a part.
Mike