So far this year, I've spent very little on books even though I usually read over 50 a year. I did have a gift card for Half Price Books which I used, and I purchased a few at a local bookstore (Dog Eared Books) for a minimal amount. Here's some of the places you can get free or inexpensive books.
Library - Your local library is great for both books and DVDs. Some libraries offer books for Kindle and other e-readers. Rather than browsing library shelves, I order them online and pick up the books when they come in. You can also order books for e-readers and you don't have to "return" - they become unavailable on your Kindle after about two weeks.
Friends of the Library - Check and see if your library has a group that raises money for library projects. They have inexpensive books for sale and may also have a yearly Blow Out Book Sale.
Amazon - Some of the used paperback books can be purchased fairly cheaply (shipping is usually $3.99). But if there is a book that I haven't been able to find elsewhere, I purchase it on Amazon using my cash back bonus from Discover (you can choose this option at checkout if your card has cashback and is listed on your account).
Amazon - There are many books available that are free for Kindle (you can also read these on your PC). Search for "Free Kindle Books" then use the drop down list to select a specific genre. (You can get an almost free Kindle device by signing up for a Visa credit card through Amazon.
Paperback swap - Exchange books you no longer read by listing books on their site. When someone purchases it you pay for shipping and receive a credit. When you choose a book to read, it is sent to you without any charge and a credit is deducted from your account.
Half-E-Bay This is a site by E-Bay that has used books for sale. You can also search on the E-Bay site for books. I purchased a large set of children's books for under $20.
Giveaways - Search blogs for giveaways. (there is also list of blogs on my Cozy in Texas blog sidebar that often do giveaways). Follow directions on blog post to enter.
Here are some of my favorite books I've read so far this year. Look at my other blog, Cozy in Texas to read book reviews.