Yvon Bourque has written extended manuals with plenty of pictures and references about the Pentax K10D, the K100D/K110D, and the K20D (link). In many ways, his books are resources that are more thoughtful and clear than other widely released 3rd party Pentax guides. He's also an excellent blogger (link) and avid photographer (link). The funny thing is, because he writes such nice stuff about this website and he's sent me samples of his work, I worry that people might think I'm gushing about his work as recompense (full disclosure: I carry a banner on this site that I designed just for him without any sponsorship obligation). Honestly, I think any underdog publisher that writes from their heart, not their wallet, about something they love deserves to have an audience. It helps that it's done well, too. Yvon is definitely worthy of the attention.
All of his books are excerpted as free PDF downloads, so you can get a taste for his writing and see if the book will be meaningful for you or any Pentax newbies you know. Here are links to the sample chapters downloads (direct PDF links).
The Pentax K20D Book Sample PDF
The Pentax K10D Book Sample PDF
The Pentax K100D/K110D Book Sample PDF
And don't miss out on his free Pentax K20D lens AF adjustment chart, to help with any AF lenses that might have front or back focusing issues with the K20D (a cropped bit is seen below). That's community spirit. It's available through his website on the front page as a free PDF download. You print it out, aim at the high contrast area with an AF lens, snap your shutter, and examine the resulting pic. So what are you waiting for?