Here is a list of projects whose documentation I found to be highly-detailed and well-written.
- The introductory tutorial of GNU Emacs (looks a lot better when run from within Emacs), is written in a very gentle and careful way; it's among the best tutorials I've seen.
- Suds - multiple, well-written examples
- rdiff-backup usage examples - much smaller than the others listed here, but nevertheless deserves mention because it's both gentle and thorough
As a sidenote, I've heard great things about Django's, but haven't really looked yet.