Yah ISBN is good, because then you can link directly to several well known book sites through just a simple url link - not that I've got a library database under construction or anything...
the only problem is the dashes.. I have a **great** book collection called soho square. The second one's number is 0-7475-0506-3 Amazon would want it in this format: http://www.amazon.com/exec/obidos/ASIN/0747505063/ where powles books want it as http://www.powells.com/cgi-bin/biblio?inkey=1-0747505063-0 . Note its only the strange whacky books which dont have images associated with them.
http://bibliophil.org/tools/isbn.asp is also a very good page if you want to make a script to generate entire lists at once. The ending idea is you only need tostore the isbn and the books location - everything else is found out for you.
J