'Normal' mouse for me.
Why? I guess its because before I used a mouse I played with the keyboard (Wolfenstein 3D and Spear of Destiny and lets not forget Doom and its sequels, those were the days ), but my first bout with a mouse with fps games, was Half-Life at a mates place.
He played with 'normal' mouse, and it just seemed logical, you move the mouse like you do in the OS.
Another mate plays with inverted, and it really screws me up playing with his config. After a while of playing with his config I cant hit the side of a barn with the sub-machine gun when I go back to my config.
Glad to see another Mr. Belvedere poll, was starting to miss them