I've found that free arts programs aren't very good, or very limited in what they can do.
I suggest you buy a tablet if you're planning on drawing from scratch on the computer, because using the mouse is really annoying and difficult.
If you buy a 'Bamboo' tablet, then you tend to get a program called ART RAGE with it, that's pretty good, and I used it for my comic.
If you want more professional looking artwork (especially if you want to do comics or just have generally good effects for artwork) then i'd suggest Manga Studio Debut 4.0. I just got it and I swear by it.
These things are kinda expensive-ish, but they'll last for a long time and are well worth the money. Othere than that I can't suggest anything!