Last summer I decided to start making ebooks. It wasn't a hobby so much as it was simply a good reason to teach myself HTML+CSS. One of my sources for content was the NASA's historical website. They've been printing books for at least 50 years now, and in mid to late 1990's most of the content was moved online. This made it really easy to download and convert.
It's a funny story how they ended up on the NASA website. After I converted my first title (I think it was a history of the Cape Canaveral), I sent a punchlist of errors I fixed (missing images, garbled text, bad links, etc) to one of the contact emails at NASA.Much to my surprise they responded, and asked for advice on how to convert the rest of the content. They said they wanted to get all of their published ebooks. I ended up giving them several of the eboosk I made. I was hoping they were going to pursue this seriously by hiring a professional (or me), but instead they've been having summer interns doing the conversions.
The 2 ebooks over on the NASA website aren't my best work, but they are okay considering I was working from webpages that hadn't been updated since 1995. I'd planned to go back and create better versions but I never had the time.