Getting ready to start my first DotNetNuke module project.  I've got everything rolling with my local DNN install but I'm looking for some best practices/reference type of information related to DNN module development.

I've found a number of documents, including here on the DNN site, but they are old.  I understand many of the concepts have carried through to DNN 6.X, but what would you recommend as the best current (or semi-current) resource as a guide to DNN core architecture, etc?

It's not free, but you can get the Kindle edition of the book Sebastian mentioned (and also reviewed, btw!) for about $15.  I did that and am running it on my laptop with the free Kindle for PC app.  Not quite as good as free, but it's a whole lot of helpful information for $15 and it will save me time enough to pay back for it in a single day.