The old ebookwise device (
http://www.ebookwise.com/ebookwise/ebookwise1150.htm) uses a very adjustable backlight/contrast setup. I usually keep mine set to the lowest brightness and low contrast, and get ~ 15-20 hours of reading on it. If I'm in the hot sun, I pump up the contrast and brightness to compensate for the temperature-caused shift in contrast on the lcd screen.
They're a bit heavier, and you'll have to convert all the books you want to read into their proprietary format (I give it about 2 minutes a book using calibre and their $20 ebookwise librarian software which I would call a must). DRM must, of course, be removed. I'd say they're a lot more techie oriented if you want to be happy with it - and no PDFs...
But it's truly backlit, easy on the eyes and readable in every situation I've tried, with or without light.
And consider how long the company might be around as well...but it is wonderfully backlit.