Turkish Grammar

This is a great reference book. It covers everything that I could ask for and provides clear explainations as well as well-thought out examples. I worked through this book and it markedly helped me with improving my Turkish. One of the better language guides that I have ever come across.

Geoffrey Lewis's Turkish Grammar is without doubt, the best grammar book for Turkish. Note, however, that it is a reference grammar not a study book. This is not the book to buy if you want to actually learn Turkish, instead it is useful to dip into for the beginner, and to study for a more advanced students. Do not use this book on its own, use it as a supplement to a study book.
For those beginning, a good place to start is Turkish in Three Months, by Bengisu Rona (published by Dorling Kindersley / Hugo). This is clear, concise and straightforward and cheap (if it is not available from Amazon, try DK direct, or second hand with ABE, or you can buy it in Istanbul).
You will also need a good dictionary, you can't go wrong with a Redhouse (which are much cheaper if you buy them in Turkey).
Probably the best and most comprehensive grammar is Turkish Grammar by Geoffrey Underhill, but it is unecesarily expensive for the beginner.
For the beginner Bengisu Rona's Turkish in Three Months is best. Once you get through it you will know where you want to go with the language (if anywhere) and what your needs are.

Turkish is very different from English. But rather than emphasize the exotic, Lewis clearly lays out the internal logic of the language, with examples drawn from actual usage.

His Teach Yourself Turkish (Teach Yourself Books) is an excellent introduction; this is an excellent reference.

About me: I never did get very far in Turkish, but I got as far as I did as fast as I did because of Lewis's books.