There are ways to sell used books that doesn't involve eBay - although that is an option. If you have a library that you want to trim down, but don't want to just donate or throw your books away, then consider ways to sell used books. The internet is making it much easier to sell used books online, but there are also local and effective ways to get the same job done.
Used Book Stores
If you live in a big city or near a big city, then there is a good chance that there is a used bookstore nearby. Check online or in the phone book for a used bookstore where you can sell your used books for cash or credit. A lot of places may give you more credit than cash for your books which can help you to expand your library collection if you'd like. Some used bookstores may also give you cash for used music CDs, records, movies, magazines, and other media - so if you are doing a thorough spring cleaning, then this may be a profitable way to go about selling your used stuff.
Powells.com is a great new and used bookstore based in Oregon. If you live in Oregon, then chances are that you are familiar with the bookstore and may already sell your books there! If you do not live in Oregon, you will be happy to learn that Powells buys used books over the internet! Go to www.powells.com and look in their main navigation bar for the "Sell Us Your Books" tab. You will need to enter the ISBN number of the books that you wish to sell and they will give you what they will offer for the book. If you accept their offer, then you're off and running. They pay you through PayPal and give you a shipping slip for your books - so no postage costs to you, they take care of everything! All you have to do is pack up your books and bring it to the post office.
Craigslist.org is an online community that acts as a classified section of a newspaper, but without the newspaper. This is a great way to advertise and sell used books locally. By advertising locally, you may be able to meet your potential buyer in a public place to exchange the goods - which reduces the need for postage or other shipping costs. If you live near a large university or school and are selling textbooks, then advertising in Craigslist.org will allow you to capture a local market that may be in need of your specific textbooks.
Yard / Garage Sale
Yard sales and garage sales are a great way to sell used books and other household items that you have been meaning to get rid of. A lot of book buyers scour garage sales in hopes of finding a literary gem to add to their collection. By holding a yard sale you will be able to clear out other clutter, besides your books. You might also consider asking your neighbors if they'd like to join in and host a larger yard sale.