Amazon has a couple more. Generally, if it's written or edited by one of the Django core devs, it should be worth the money. But pay attention that you don't buy an edition for an obsolete Django version (e.g. 0.96)
Like others said, the official documentation is top notch, and #django on freenode and the mailing list can help with specific problems
And the second question:
before developing an app yourself, look if there isn't already something similar on Google Code, GitHub or Bitbucket. There's an incredible number of useful django apps around
The Django site provides a tutorial on how to build a poll, which can be easily modified to build a blog. James Bennett's book, Practical Django Projects, also explains in significant detail how to build a blog/cms.
As for books:
And the second question:
James Bennett's Practical Django Projects does a pretty good job of covering those topics in general and even includes a chapter specifically on "Writing Reusable Django Applications" that goes through an example of splitting one of the example projects in the book out into its own app.