Digital Book Readers

A digital book reader, also called  e-reader, is an device that is designed primarily for the purpose of reading digital books and periodicals and uses e-ink technology to display content to readers.
The main advantages of these devices are portability, readability of their screens in bright sunlight due to the e-ink, and long battery life.
Any PDA capable of displaying text on a screen is also capable of being an e-book reader, but without the advantages of an electronic ink display.

If there's one digital book readed you must know, i think it would be the Sony PRS-505.
Here's why :

•  It's NOT LCD screen
• He's got a nice large screen
• Easy to read display - e-paper display with quicker page turns
• Premium design - Simple, yet sophisticated with easier navigation
• Compact and lightweight
• Integrated eBookstore with 20K titles
• Up to 7,500 page turns on full charge

Even, you can search for some reviews trough Google, and if you don't ever know what to buy , there is a huge list of Digital Book Readers so, I won't remake the world as there is already a Digital book readers comparison, so just have a look at "Comparison of e-book readers" on Wikipédia.