Although I don't know of any others, I created a 
pricing type guide back in april in the 
Rubberslug.com resource section.

http://www.rubberslug.com/resource/guide_info.asp?
GuideID=22

Remember though, these are all MY opinion, based 
on what I have sseen. There is really no sure-
fire way to know *exactly* how much your cel is 
worth unless you try selling it. And even still, 
demand changes over time. 

Good luck ^^
~Tara