PDF形式の書籍購入サイト

▼InformIT: The Trusted Technology Source for IT Pros and Developers
http://www.informit.com/

▼オーム社eStore(β)
http://estore.ohmsha.co.jp/titles

▼O'Reilly Japan Ebook Store
http://www.oreilly.co.jp/ebook/

▼Ebooks-O'Reilly Media
http://shop.oreilly.com/category/ebooks.do

▼Apress
http://www.apress.com/

▼The Pragmatic Bookshelf | Our Titles
http://pragprog.com/titles

▼Home | Packt Publishing
http://www.packtpub.com/

▼洋書（開発本）のイイところ - Good things about English books - iOS 開発ブログ Natsu's note
http://blog.natsuapps.com/2011/06/good-things-about-english-books.html