I am not trying to find out what library i should use (I've used them all now) but I just wanted to know what is most popular at this site (please don't post too much info on your choice, that always leads to arguments). If you use more than one library but one outweighs the other just vote for the one you use the most.
SDL. (post like this)
Oh and to prevent people asking for tons of links in this post:
-DirectGraphics (Graphics portion of DirectX) http://www.microsoft.com
-Allegro http://www.talula.demon.co.uk/allegro/index.html and http://www.allegro.cc
-OpenGL http://www.opengl.org and http://nehe.gamedev.net