Kindle Paperwhite, or other ereader
You can't go wrong with Amazon ereaders. I have a first gen Paperwhite and I absolutely love it. The built-in light is really nice, the display excellent. I have the one without special offers but if you don't want to pay extra then it's fine because the ads don't interfere with your reading at all. The 3G feature (if you get the 3G version) is really cool, you can buy books on the go. The battery is outstanding, my Paperwhite lasts for about a month without charge, but I almost always have Airplane Mode turned on, so that really helps.
BTW, if you end up getting one with special offers, and you later find them annoying or something, you can opt out by accessing your Amazon Kindle account online and paying $20. And yes, Amazon IMO is the best place. They have the best collection of ebooks and their customer service is amazing. Do not buy ebooks from Kobo. Almost all of who did have had bad experiences. Very poor CS.