Greetings from frozen Minnesota! I have been indulging in the used book websites for about a year now, and have had wonderful luck in filling out my book collection, at the expense of my bank account. I've ordered song collections from bookstores in the US, Canada, France and Australia, a found wonderful things. At the risk of giving myself more competition, here is a good link to multiple used book search engines:

http://www.rarebooks.org/searcheng.htm

Rarebooks.org is also a good site to learn more about book collecting in general.

Now if I could just find a copy of volume 1 of Bronson that doesn't cost more than my house...