I've recently bought Brewing Classic Styles: 80 Winning Recipes Anyone Can Brew by Jamil Zainasheff and John Palmer - it's good because it runs through a load of beer styles, recommendations for the style, tips on making your own recipe along with a recommended recipe. Interesting to have on hand for putting recipes together!
I've also got IPA by Mitch Steele and The New IPA by Scott Janish - both interesting books. I'd recommend IPA by Mitch Steele as it goes in-depth on history and has a lot of old and modern IPA recipes in it! The New IPA is very science-y, but has a lot of interesting info in it!