there are 100s of such services out there (most query many more retailers to find the lowest price) + some offer API access so you can do revenue sharing.
the biggest player in the space is http://bigwords.com
the biggest player in the space is http://bigwords.com
bigwords.com also only seems to work for textbooks.
For a timesaving tip, you can type any ISBN or keyword (title, author, etc), directly into the URL to save a few seconds. IE:
http://texts.com/b/Steve Jobs Walter
>>
http://texts.com/b/Steve%20Jobs%20Walter
>>