The Beckett Pokemon Collector Price Guide Magazine has always been one I've used, and that many collectible stores that I've gone to have also used. It specifies every set, with each card and indicates their individual price and rarity! I'd recommend ordering an edition if you want to see how much your cards are worth. If you are trying to put your sets/cards in order, it's also a very helpful source, as the card scans on the main PokeBeach page is also! If I'm correct, Beckett also has an online site as well!