I noticed this post on the Dear Author blog that lists things authors do on their websites that book sellers and readers hate. It makes some good points, a lot of which I would never have thought of. I think authors assume it's only fans who are looking, and fans probably don't care about ISBNs (except those of use who are Former Librarians). One suggestion is to have a printable list of your books--makes sense, doesn't it?
Even the comments are quite useful, especially the one about ways to make your site more accessible to the visually handicapped.