So I just recently got the Nook 2nd Generation E-Reader ("Nook Simple Touch"), rooted it to access the full Android 2.1 below, remapped the hardware buttons, and finally, decided to replace the shitty built in screensaver with some better ones.
Unfortunately, I found it hard to find pictures that were already formatted for the grey-scale of the screen and the Nook's 600x800 active resolution (the Nook Simple Touch has a physical display with a 4.8 inch height, 3.6 inch width, and 6 inch diagonal), so I took some of my desktop backgrounds, in addition to some new pictures I found, and formatted them in Photoshop. I think they look pretty good as Nook screensavers, so I figured I would share them with the internet too. These should also work well as Kindle screensavers, or any other E-Reader out there.
If you want to bulk download all of these, I suggest going to the Picasa Album I have them posted under and clicking "Download to Picasa" under the "Actions" menu. Of course, you will need Picasa to do this, but really, you should have Picasa anyway; awesome program for sorting and viewing pictures on your computer.
I also have the pictures embedded below, after the page break. Click on the thumbnails for the full resolution versions and a Lightbox slideshow view.