<p>I'm not a member of this community, so I'm going to throw this out as a suggestion and see how many votes it gets.</p>

<p>Consider linking to <strong>isbn.nu</strong>, which queries a number of online booksellers and shows prices for all of them. (<a href="http://isbn.nu/978-0-701-18390-5" rel="nofollow">My current reading</a>.) This is always my own choice these days, on Stack Exchange or elsewhere.</p>

<p>Be aware that <a href="http://meta.stackexchange.com/questions/26964/auto-inserting-stack-overflow-affiliate-into-all-amazon-book-links">links to Amazon have the possibility of raising money for Stack Exchange</a>. Whether you think that’s a point against them or a point in their favour is up to you.</p>