The MobileRead Wiki has an excellent matrix showing all the available electronic reading devices as well as a picture and details for each one such as:

• Display size
• Screen refresh time
• Battery life
• Weight
• Operating System
• Memory
• Support formats
• …and much more

Preview:

Many people have heard about about ebook readers but don’t know:

• What companies make these devices?
• What models are available, their features, and the pros & cons of each?
• Where to buy them?

Let’s start by looking at the current list of companies/models of e-book devices:

• FLEPia by Fujitsu (April 2009)
• Kindle 2 by Amazon (February 2009)
• eSlick by Foxit Software (2009)
• PRS-700BC Reader Digital Book by Sony (October 2008)
• Digital Reader 1000 by iRex Technologies (2008)
• Kindle by Amazon (2007)
• Cybook Gen3 by Bookeen (2007)
• GeR2 by Ganaxa (2007)
• Star eBook STK-101 by Star eRead (2007)
• Hanlin eReader by Jinke (2007)
• Sony Reader by Sony (2006)
• iLiad by iRex Technologies (2006)
• Libri� by Sony (2005)

Source: Wikipedia

As you can see, Sony pioneered these devices in 2005 which opened the doors for some healthy competition since then.

Note: There are other Ebook Readers available on the market but they have simply been rebranded from the original units listed above.