Debuggers

[Syoma]

Visual Studio (+ VisualDDK for kernel mode debugging).

I see there is no problem which debugger we must use
the important thing that you must know how to use the debugger in a correct way
I use OllyDbg

[Evilcry]

Sure,
just remember that gdb comes out from porting issues and for its particular
structure is slow.

IDA Debugger is great and presents the advantage of plugin integraton,
this thing is really important because allow you to harden debugger from
hostile code

thanks ahmadmansoor !

[bedrock]

ollydbg is good, and easier to learn, but will become less useful as more people move to x64, i for one have already installed Windows 7 x64 version on my laptop, it will be my only OS (apart from VM) from now on...

[lordnasty]

IDA + Ollydbg
Olly for a "fast" debugging
IDA for a deeper work
Using together, however, is the best (example generate file .map with IDA and then pass the .map file to Olly and continue works on the same target).

IDA for static analysis

Debuggers
Windows
Olly for Ring 3 Apps
Softice/Windbg for Ring 0 code
Immunity Debugger (olly+python) for quick exploit writing

*nix
gdb + a nice gdbinit script
IDA Debugger (remote ) + gdbserver [ this is quite nice actually]
kgdb for Linux kernel debug

Speaking of a GDB init file, mammon's gdbinit is pure jewel.

http://www.802.11mercenary.net/~johnycsh/misc/mammon-gdbinit-fixed.txt