Online Book Sources

www.usedbooksearch.co.uk (a meta search engine for finding used books, textbooks, antiquarian, rare and out of print books)
www.usedbooksearch.net(The sister site to usedbooksearch.co.uk, on which prices can be compared for specific book publications)
www.aslanchristianbooks.com (new Christian books)
www.authenticmedia.co.uk
www.abebooks.co.uk (new & used books from many sources)
www.10ofthose.com (cheap bulk orders)
www.clcbookshops.com (CLC)
www.chbookshop.co.uk
www.eden.co.uk
www.getfreeebooks.com (Free eBooks) 
www.kingdompublishers.co.uk
www.kitab.org.uk (books on Islam)
www.lovechristianbooks.com 
www.standrewsbookshop.co.uk
www.thegoodbook.co.uk (good for Bibles, studies and course materials)
www.missionbooks.org
www.book-aid.org (used Christian books)
www.amazon.co.uk (new and used books sold through Amazon) 
www.123PriceCheck.com