I used to run a new thread with this title every day. Why did I stop?
The Booksellers forum is a terrific resource for all of us: pros, amateurs, hobbyists, philes, etc. There is someone here that can answer just about any question you may have about any aspect of books or the book business or eBay or taxes.
To start with, if you want to know the comparative value and/or the basic information about your book, try
www.addall.com/used/ first. This is a sort of bulletin board that lists millions of books for sale by anybody with a computer on the Internet. But beware of any and all information you may harvest in this manner, because there is no vetting.