For my the best option it's IDA + Windbg for analiysis drivers and malware and everything else Olly :)

Sometimes, I use PEBrowseDbg to debug .NET apps.

I use integrated IDE debugger to debug apps. Ollydbg for sometime.

added:
DOS = TR :D

Me, I prefer Ollydbg, cause it has become quite popular, even replacing softice. It's free and has trumendous support especially for scripting; you can find a lot of ollyscripts for unpacking protections for example.
IDA on the other hand is quite powerful for disassembling (windows/non-windows binaries) and can do a fair job for debugging. I use it for remotely debugging linux apps too.

Note for SquareD: graphs in IDA are annoying indeed, but you can disable them. Right-click in the IDA-View window, and select Text View.

In Windows, I use Visual Studio to debug my programs and Olly and IDA to debug others.

GDB and DDD are my choice of debuggers in Linux platforms.

I think Ollydbg is best for unpacking.
When will the Ollydbg 2 be released?

There was nice TRW2000 debugger for Win9x systems. Very useful for those familiar with SoftIce ;-)

Olly is handy for processes that are running where you also need to look which memory is used by what, so handy for packed programs and so on. Windbg is usefull for drivers and other such stuff. ida is awesome for understanding the codelogic and the disassembly, the debugger is fine too. ida can handle pocket pc exe's, linux exe's and images of various other kinds where other debuggers simply give up.. So ida is a must have for strange platforms (for example nds and so). But for strange platforms there is also codewarrior but disasembly with that and trying to understand what goes on is harder with that. I only tried it once or twice or so, likely it is way better now...

If you're a python fan, there's also Immunity Debugger (Ollydbg+Python, really) and PyDbg for coding things quickly.

Yes!! I miss this wonderful debugger. Liu Tao Tao has created small, good and eficient debugger.

Tiny nitpick.. but DDD ain't a debugger. It's just a frontend to GDB.

what a bout debugger for x64 ...any one know Good one ??
soon or later x64 will come !!!

windbg... that's all folks :)

Agree, WinDbg does everything.

Git