I loaded up almost a hundred books to my Kindle from Project Gutenberg. There are other free (legal) eBook locations such as Baen Free Library. For the $80 Kindle, that's likely worth it, even without accessing the vast illegal (in the US at least) sources. I agree they're definitely bad for PDF, text books, or anything else you'll want to flip back and forth; only good for sequential reading (novels and the like). They're very reliable and last a long time.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: