Kindle DX-
Pro:
Large screen
Supports PDFs VERY well, as well as the mobi files
Access to Amazon's ebook store (can't be stressed enough. Content is king.)
Long battery life (not sure how much actual usage - but long!)
Free internet access, decent (if slow) browser, wikipedia, etc.
Online web store
Nice 16 shade grayscale screen, very clean and crisp
Dictionary
Annotation and Highlight
Search
Can send things to kindle in pdf, mobi, doc, or html format
Not too heavy
Cons:
Still a bit high, price wise
Only mobi and pdf's
No organization of files (well, hardly any)
Sprint coverage can be a bit spotty, also it's Sprint and that sucks on principle
Fairly closed system
I'm sure there is more... but it's almost 5 am.