I've been keeping my cel-related info in a simple
AppleWorks database. A record includes, among
other things, the series name, characters, what
scene it's from (if I know), who I bought it
from, its list price and actual price (includes
any discount, tax, shipping, MO charge), cel 
numbers, whether it has a sketch, a background,
is oversized, its general condition, how many 
layers and whteher it's a key cel or not. (Whew.)
At least that was the plan. I don't always enter
all the data and, sometime a few years ago, 
some data mysteriously vanished from some fields,
never to be replaced. I can sort the database
various ways and get summaries by title, dealer,
date, etc. More info than I want to see, actually.
Especially the total price of a thousand-plus
cels.... ^_^