If you're talking about strategy guides, then a simple title search in Amazon should do it for you most of the time.
When buying, be sure to compare between auction sites like Yahoo and eBay and retail sellers like Amazon and alibris.com. Depending on their age, popularity and availability, the prices between buying or waiting on an auction may vary. Sometimes a guide you'll find on Amazon for $35 pops up on eBay and you can win it for $15. Also with eBay, sometimes you'll won't find a guide listing, but a game+guide listing.
I'm kinda building a wiki listing guides per game and maker, but it's far from completion.
Feel free to check it out.