I usually buy play scripts at used bookstores (there are tons of them here). But I usually haunt Barnes and Nobles. For Christian stuff, I go to Lighthouse.
I buy most Christian titles from Amazon, as they support many authors that the normal bookstores do not carry. You can find plenty Christian fiction and non-fiction by searching Amazon's categories.
Occasionally new books from Amazon.com or Christianbook.com. But mostly, used books from Amazon new/used or Half.com. Over half the time the postage costs more than the books!
Usually either Barnes & Noble or Redding Christian Supply, both here in Redding. In the last six months or so, I've ordered several books through christianbook.com . And I like to haunt used book stores wherever I go! Ya never know what yer gonna find!!
Usually the local Christian bookstore or Christianbook.com. I also browse used stores, local library sales, yard sales, thrift stores to see what I find. I'll hop into B&N once in awhile if I'm looking for something specific or on hobbies and such.
If I simply must own a book, I purchase it on Amazon used. Generally I borrow books from friends, or if I intend to read thru it quickly, from the library. For the most part everything I could possibly care to read is online anyway.
I either go to Powells, or Barely Read Books.
Barely Read Books is great. I went there the other day and they where having a sale for some books that they didn't think any one would want for 30 cents a piece, so I got three books for 90 CENTS!
Both places are used book stores, but powells sells both new and used.
I get most of my books from the library these days, but I do have a fondness for browsing hole-in-the-wall used bookstores! If I'm looking to find something online, I'll use Ebay or Advanced Book Exchange (http://www.abebooks.com)...