In general, I don't buy that many books - I get them from our excellent King County library system. However, once I've gotten a book more than a few times from the library, I'll buy it.
When buying books, I look first for used books on Amazon.com. I've had nothing but good experiences doing this, and frequently, when a book is not in high demand, I can get it for very little.
There's definitely a few tricks that you can use to get a better price, though. For instance, recently (July 2010) I wanted to buy the book 401 ways to get your kids to work at home. Looking for this title on Amazon, the used copies were 11.89. Not all that cheap, considering it's a paperback, and shipping is not included.
However, this was not the only copy of the book out there! Older editions may go for much cheaper, but you need to know to look for them. Sometimes, like for this book, there's a tiny little box that shows all the formats available. In the case of this book, there was a paperback edition from 1981 that was going for $.01! Just $4.00 (plus shipping of $3.99, which is where the seller actually makes some money). That's the edition I had gotten from the library anyway.
Other ways of finding these older, but still almost (or actually) identical editions are by searching on the author's name, and not just the title. Sometimes different and cheaper editions will show up there as well.
Just a few more clicks and you may be spending drastically less on the same book!
