I just picked up 4 Abeka books over at Paperback Swap.  If you select the browse option, you can choose to search under the special "Homeschool" topic.  I browsed through and found several items that would make a nice complement to my hs library.  But I stopped at 4- spending almost all my credits.

In the non-homeschooling area, just searching Children's Books will give you lots of living books on history and science.  I've collected quite a few of these over the past few months too.  I also have been very blessed to find great kids' devotionals at Paperback Swap.  I've not looked for adult ones, since I find so many of those at my local library sale but I'm sure there are many listed.

Anyway, since I found so many homeschooling books when I was browsing, I thought I'd remind everyone of this option.  Click the banner to get to the PBSwap site:

If you are new to Paperback Swap, just post 9 books that you are willing to trade and you'll get 3 free credits.  You are responsible for paying postage whenever anyone requests a books- this will cost you between $2.13 and $3.00 depending on the size of the book (most are in the $2.13 range). 

To make things easier on myself, I bought a package of manilla envelopes and some packaging tape and keep stamps on hand in various denominations to ship my books.  I also use a small scale to check the weight.  If the book weighs less than 6 oz. it's cheaper to ship first class.  My Post Office also has a 24 hour kiosk that allows me to weigh books and then purchase postage.  It doesn't do media mail specifically, but if I know the correct postage I can purchase a plain stamp in that amount and still send my book media mail. 

Be sure to check under the Community listing to access the Discussion Boards.  There's a forum called Book Bazaar where people often post 2 for 1 or better deals.  I been able to get 4 children's books for 1 credit on occasion.  The Abeka books costs me a full credit though.