I found some screen protectors and even skins for the two smaller Kindles (Invisible Shield has them, for example). For the DX, I just did a
search and got this
Boxwave link first, which has two kinds of protectors (one is supposedly anti-glare). Another option is to buy a screen protector for a netbook and just trim it to fit.
edit: for the record, here are two places that make skins for the Kindle 2 (so it's a fair guess they'll get to the DX eventually):
InvisibleShield and
BestSkinsEver. I've never used any of these, though
edit #2: The reviews for the BoxWave shield aren't so great:
http://www.amazon.com/Amazon-Kindle-.../dp/B001ACNN9W