I use CorelDraw, which is a vector-based program like Inkscape or Adobe Illustrator. (Or Xara, which I haven't tried, but have heard good things about.)
Vector based programs fit the way my mind works. I have troubles when I try to use Photoshop or any other paint/bitmap type program to create drawings. Most other people seem to be the other way around.
Let me add: If you're at all serious, get a tablet. You might be able to manage without one if you find you prefer a vector-type drawing program, but even there a tablet is useful. If you go with a paint/bitmap program, a tablet is a must. A basic Watcom tablet will set you back by ~$100(US), but comes bundled with some basic paint programs (e.g. an older version of Photoshop Elements, plus one or two others.)