Search facets are likely the best and fastest filtering mechanism for the users. It's pretty much just a straight products site with some recommendation engine. Just start faceting out the books by a few criteria, topic, length, proficiency level, etc.
The autocomplete is fancy, but it involves: a) typing; b) spelling; and c) using the arrow keys and the enter key. Facets will let you get to the same place in a few clicks. You can always do both, though.
