I took my digital camera to a decent plastic skull and made myself a stack of worksheets. Whenever I get a free moment, I grab a sheet and draw what's on it. I try to slip in at least 10 a day.
See that plastic box in the upper righthand corner? It's a disarticulated skeleton. I plan to visit every major bone in the body. Just as an exercise.
UPDATE 10/1/2009 - old link replaced by new one
The skulls are here on flickr if you want to try the same thing yourself.
i just wanted to write a quick note to thank you for posting the skull photos on your site! i did not realize until recently how important it is to understand the underlying skeletal structure of the human body in order to accurately render it on paper. =)