Well, after spending the morning working on trying to whittle down my lists I think I've decided to hit it from a different angle.
I was grabbing random products, which just wasn't working, so here's my newest thought:
I'm going to separate the books into pile by type of product, Supplement, Adventure, Adversary, Setting, Aid, Mini, Regalia, Software, Free Product, Electronic, Game, and d20. That way I'm at least comparing apples to apples.
We'll see if that makes it any easier.