Cels Forum

A lot depends on the style of character you want.
Gowcaiser and Virus are definitely from a destinct art style.  

Some series that come to mind are:

Gundam Wing
Slam Dunk
Marmalade Boy
Yu Yu Hakusho
Street Fighter

You could also try collecting Dark Schneider from Bastard and Fushigi Yuugi cels seem to be getting cheaper. If you ever decide to move to a higher price range, I think that X cels are consistently some of the prettiest cels around, both the guys and girls.

Good Luck 
Dave