On freelanceswitch.com you can find a good read on hw to charge your client for the services you deliver (got it via a friend who is a free entrepeneur and a PhD as of yesterday). While all that is said in the posting is true, the best remark came from Michael Martine:

Slap the client in the face as hard as you can, then tell him your rate. If he’s shocked that you slapped him, you’re not charging enough.

(from Anil Dash. Sounds like fun, happy slapping!