Now you can download a variety of formats of the complete Digha Nikaya, the Long Discourses, translated into English by Bhikkhu Sujato for Sutta Central. They are available for free distribution. If you find any errors, please report them directly to the SuttaCentral.net discussion forum.
If you are going to use the ebook edition for a daily sutta reading practice, you may want to use a checklist to keep track and have a physical reminder of what you have read. You can download checklists here.
And of course you can read it on-line at SuttaCentral.net.