Unfortunately is not so easy to find books about Estonian language in English.
E Nagu Eesti
The first Estonian language textbook and most used by foreigners to learn Estonian. All his 30 chapters doesn't have one single word in English, but includes a useful Estonian dictionary (Estonian to German/Russian/Finnish/English). NB! It requires a teacher (or a Estonian friend) to understand its lessons. Can be found for 12 euros in TEA (Estonian Publisher / Language company).
This book is used by Tartu University foreigners that want to learn Estonian for entering Estonian courses in University (in other words, its the best available). Includes a CD (50 minutes) with sound exercises, and can be found for 20 euros in Apollo (one of the biggest book shops in Estonia).
First book made for English speakers, with many explanations about Estonian grammar. It starts easy, with English translations till chapter 5. Then Estonian is more used. The book has an audio CD (sold separately), and can be found in Amazon.com for around 35 USD. This book is commonly found at public libraries in Estonia, so you can try it before you buy it.
Teach Yourself Estonian
From the same authors of 'Naljaga pooleks', a self study textbook for English speakers (not available yet), pre-release listed in Amazon.com for 35 USD (I believe that it will be better than the above one).
As far as I know, there's many books for Germans and Russians to learn Estonians
(basically because of historical reasons). There are many dictionaries available also between those languages.
If you happen to know the name of a good book for learning Estonian (in English, German, Russian or any language) feel free to add it in the comments.