Since your target market is web developers and designers, I suggest you start with some books on subjects that those people are likely to be interested in. Clearly, that would suggest books on web development and design, but it might also cover SEO, programming in general, typography, social media, and similar subjects. If you search on the relevant keywords in Amazon, you'll come up with plenty of possibilities.
When choosing books (or any other product) to link to, make sure the book is currently available (no point in linking to items that are out of stock with no indication of when they will become available again). It should also be up to date (check the publication date) and of high quality (read the reviews).
Keep in mind that you don't have to choose specific products to link to. Amazon have a number of widgets that will recommend books or other products based on keywords that you specify. This process is clearly explained on the affiliate site.