I love my Kindle 3, but wouldn't recommend one for viewing PDFs - the screen is too small. The DX has a bigger screen, but the PDF support is not as good in that model, and there is no telling if the software will be upgraded to the same level as the Kindle 3.
A device with an LCD screen (for faster display) that has larger than a 6" screen is probably your best bet, if you can afford it. I don't have such a device myself, but I have seen coworkers use PDFs on ipads, and it looks great.
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