Jessica Hische is an illustrator, typographer and designer whose work I've peeked in on from time to time over the years and have great respect for. Her site entitled "jessica hische is awesome"... is by no means false advertising.
She devised this amazingly funny (and truthful) "should I work for free?" flowchart that's pretty great.
I need to get a print of this at some point when I have wall space again... and when anyone asks I can point to it and wear a knowing grin.
While researching articles on licensing artwork and the "business" of art I came across and article she wrote that I found not only helpful but a great read.
If you're just getting started out, have been around for awhile or just want to learn something- take a gander: On Getting Paid