Delphi: DeDe, free, produces good quality source code.Visual Basic: VB Decompiler, commercial, produces somewhat identifiable bytecode.

You'll have to look around to find the best version. I believe W32Dasm is abandonware these days, and there are numerous user-created hacks to add some very useful functionality.

W32Dasm(free) - a bit dated but gets the job done.

Costs quite a few bucks though (there exists free version, but it is quite quite limited) Used by most professionals, like malware analysts etc.

IDA Pro(commercial) - top of the line disassembler/debugger.

SoftICE is still used by many professionals, although might be hard to obtain and might not work on some hardware (or software - namely, it will not work on Vista or NVIDIA gfx cards).

SoftICE is kind of a hardcore tool that runs beneath the operating system (and halts the whole system when invoked).

Commercial and development stopped in 2006. WinDbg is especially useful for looking at the Windows internals, since it knows more about the data structures than other debuggers.

WinDbg, free, a quite capable debugger by Microsoft.

OllyDbg, free, a fine 32-bit debugger, for which you can find numerous user-made plugins and scripts to make it all the more useful.

DIE has a strong developer community on github currently). With a decompiler, you can turn a program back into partial source code, assuming you know what it was written in (which you can find out with free tools such as PEiD - if the program is packed, you'll have to unpack it first OR Detect-it-Easy if you can't find PEiD anywhere. With a disassembler, you can view the program assembly in more detail. With a debugger you can step through the program assembly interactively.

Disassembly free instal