Years ago, I started to maintain a list of services that could take an ISBN in a URL to look up stuff about a book… OUseful ISBN Playground:
I really should update this service, so if you know of any online web services that take an ISBN as a URL argument, or maybe a Linked Data SPARQL request that searches around ISBNs, please let me know via a comment to this post, and I’ll have a go at updating the ISBN Playground:-)
Related: Dewey Fencing, and Getting Started With Bibliographica Linked Data
OUseful.Info, the blog... 
http://isbn.net.in/isbn
– shows comparison prices in indian rupees and also some other info like reviews
Wikipedia:ISBN
“The MediaWiki software automatically recognizes inline International Standard Book Numbers (ISBNs); for example: the wikitext ISBN 978-0-12-345678-9 becomes ISBN 978-0-12-345678-9 which corresponds to Special:BookSources/9780123456789. (This is a form of WikiMagic.)”
Tim Spalding @LibraryThingTim on Twitter would be a good contact on this topic I think. Librarything – http://www.librarything.com
Lots of library catalogues of course – but Worldcat (worldcat.org) and Trove (nla.gov.au) are two that would be worth considering.
BookButler (http://www.bookbutler.com/), an invaluable price-comparison site offers ISBN look-up.
I’ve been trying to maintain a list of as many useful services as possible (for mashing purposes) at: http://jerome.blogs.lincoln.ac.uk/2010/07/21/linking-university/ – many of which will take an ISBN…
…how about the Talis Platform UK bib store?