SDL. The one, the only. I have tried allegro a little bit, way back when. But SDL makes me happy.

Allegro. I like the library for it's ease of use, features and the help/information available on Allegro.cc

I'm open to trying other libraries in the future though.

SDL, OpenGL and Freetype.

I've also used ODE in the past.

Glfw and Audiere.
I want to use a complete engine later too. NeoEngine 1 probably.
I just don't understand the open source engines well enough yet.

I use ClanLib and OpenGL to write a shoot'em up game engine (and editors, and a game using it,etc).
If you have never taken a look at ClanLib, it's worth the effort I think ^_^.

Here for the CL : www.clanlib.org
and there for Prelude : http://prelude.servegame.com.

Rendering: Ogre
Scripting: Lua with LuaBind
Physics: ODE
AI: NeuralFuzz (My Own)
Sound: OpenAL
GUI: CEGUI (Crazy Eddie's GUI MK II)
C++ Goodies: Boost & STL
Image Manipulation: Devil

The above post was me.

GLFW
Lua
OpenGL
OpenAL
zlib
libpng
Torque Game Engine

not libs but included with them:
C++(digitalmars and mingw)
D
python

SVGAlib
Linux fb - No I'm not joking.
The reason is that they performs better than SDL on my P100.

SDL for graphics, input, timing, etc
NerveBreak for scripting
pretty much nothing else for now, but i'll probably use SDLNet for networking and OpenAL/OGG for audio :-)