There are quite a number of guides about Crete to choose from, both general travel guides and some specialized in walks. Apart from these, you can find many historical books, travelogues, novels set in Crete, cook books and more.
You will also find a number of maps. Many of those are adequate for driving around in Crete but unfortunately there are still no good large scale walking maps except for some regions of western Crete and the mountain range of Psiloritis.
Please go to the following pages for more details.
You can find many books and maps in the larger bookshops in Crete - located mainly in the cities and some tourist resorts - but don't rely on what you want always being in stock. To play it safe, buy before you come to Crete.