OllyDbg is a good free binary disassembler/debugger
http://www.ollydbg.de/ -------- Ida Pro is a very nice disassembler/debugger -- (its commerical but it there is a free windows version)
http://www.datarescue.com/ http://www.datarescue.com/idabase/idadown.htm -------- W32Dasm is a decent (kinda old) disassembler/debugger -- is it still commerical??
(look for a demo via google) -------- REC is an impressive free deCompiler (better than a simple disassembler) its based off of boomarang http://boomerang.sourceforge.net/ (notice http://www.program-transformation.org/Transform/DecompilationPossible ("Pigs from Sausages?" hehe http://www.dur.ac.uk/martin.ward/martin/papers/migration-t.pdf))
http://www.backerstreet.com/rec/rec.htm
I hope you find this helpful -- I have some other links up my sleves but most are outdated and or commerical
Nick