http://chamberfour.com/ereader-comparison/ (long, discusses mostly non-Kindle/Nook eReaders!!)

http://www.barnesandnoble.com/nook/compare/index.asp (comparison by B&N)

http://venturebeat.com/2010/01/30/e-reader-comparison-chart-6-readers-19-features/ (convenient chart)

I also recommend looking at the websites of the producers themselves and comparing that way