I found a neat little site (thanks to Holly) that will be of interest to readers, it's called
Read It Swap It. You join and upload a library of books that you have and no longer want to keep, other members might browse through your library (or find it due to searching for a particular book which you may have) they then send you a request to swap that book and show you what they have in their own library. You decide if there is something of interest that you like and agree to the swap (or not). If it is agreed then you just post your book off and wait for the one you swapped it for to arrive. I've just done my first swap and have been told the book should be here about Thursday, cool!
You can also search for titles that you want, make a 'want list' and if they should appear on someone's library list you will be informed. Very handy little site... and free!