Philip Waldron recommends: I'm not sure what kind of target audience you have, but I'll assume that the bulk of your book buying population are going to kyu-level players. Here are some books that have impressed me over the years and should sell quite well:
I'm afraid much of the list is biased towards Kiseido because that is what I learned to play go with. On the other hand, they've also been in business a lot longer and have had the opportunity to put together a very good selection of books in their catalog.
I have also heard good things about the Samarkand Learn to Play Go series, but I haven't got copies so I can't comment on them directly. Similarly for a number of Slate and Shell offerings, particularly those by Richard Hunter. Slate and Shell's Dictionary of Basic Tesuji has received good ratings on GoDiscussions, but I was involved with proofreading the series and wouldn't feel right passing judgement.
If you want to aim for players a little stronger (strongish kyu and dan-level), I can also highly recommend a few more books:
Two other thoughts. If you don't mind stocking foreign-language books, I can strongly recommend:
These are problem books and are accessible to players with no foreign language skills. If you have to pick only one, get the Segoe tesuji set. It is absolutely brilliant and doesn't get nearly enough press in the Western world.
Finally, you might consider picking up a few issues of Go World magazine from Kiseido. They are well regarded and should sell quite well and there may be back issues still available on the cheap.
I'm afraid I can't recommend a really good introduction book because I learned before most were published. Janice Kim's Learn to Play Go series seem to be well respected, but perhaps others on the forum can provide some feedback.