The kindle BASE version, has no audio so if you are into audio books, keep that in mind. It also has no touch screen or keyboard, so to browse their online store you have to do the old NES typing and press the to navigate an on screen keyboard. Also, to get the $79 version, you have to accept advertisements as a screesaver/at the bottom of the screen when you shop, otherwise the cheapest is $109. Unless you find one on sale.
The nook has a touch screen menu at the bottom and audio, it also supports EPUB format (first edition does anyway, not sure about all editions) – so you can use most FREE ebooks on it. It is $89 for the 1st edition. It’s also supporting B&N which means the brick & mortar stores get a little boost even though you are buying e-books.
Both have some free books available. Both read project gutenberg books. Both use e-ink. Both use a flash system to make the slight lag e-ink causes to seem less. Both have a big selection. Both have wi-fi. Both use a laser based touch system, which some people find annoying for their touch. They are pretty similar at the moment. B&N lowered its prices for e-books to match kindle, so most of them are the same cost. Both e-readers are fine quality and mostly have the same features and only a $10 difference between their two base models.
My biggest problem with kindle is… I really, really do hate supporting Amazon.com. They until recently sold illegal animal fighting magazines and videos, including magazines that were basically catalogs for buying animal fighting supplies and the HSUS also ordered these for their investigation and animal fighting RINGS complete with bought off police were uncovered in the advertisements in them. Amazon.com refused to stop selling it until the US Postal Service took a step towards not shipping these items because they are against Federal Law. The HSUS was winning its court case, so Amazon took the items off and most the magazines are no longer being published. But, Amazon took them off with the “We have the right to sell these” as the last word.