Today I’m writing to recommend the Amazon Kindle. There are two versions, one with WiFi only:

and the Wifi + 3G (Sprint) version:

There are a few devices out there to read books on. However, none are quite as good as the Kindle.
The nook is very similar, but the screen does not refresh as quickly as the Kindle. The iPad has a very large disadvantage (as does other Tablets) in that the screen is LCD based - in other words, light is coming out of the device to you - and is stressful on the eyes. The Kindle, on the other hand, is reflective, like paper, and therefore is easier on the eyes, and allows you to read longer.

Another cool invention that the Kindle has is WhisperNet…With the 3G version that’s how you download the books to the device, or get newspaper content on the device. It also keeps the page you are on in sync across devices - multiple Kindle devices, a PC reader, Android, Blackberry, iPhone, or even the iPad.

Whether or not to get a e-Reader in the first place is a question you’ll have to answer on your own. It’s much lighter then carrying multiple books. The electronic versions of the books are not perfect - they sometimes have spelling errors for example.

For more information about the screen of the Kindle vs the iPad - see this article:
Kindle vs iPad under Microscope