http://www.artmarketplace.com/dictionary.html is 
a nice reference page for cels (not just anime 
cels).

I still need ID help with some of the Tenchi 
cels.  I have never seen Pretty Sammy before 
(since it's not out on DVD yet), and some cels I 
labelled as Pretty Sammy because that's what the 
retailer told me or it's because I've seen 
similar screen captures on web sites.  If any of 
you could tell me what's going on story-wise with 
some of the cels, that'd be great.  Thanks.