What are the best resources for Wordpress theme-development? I am currently in the phase of starting my own blog, and don't want to use one of the many free themes. I already have a theme for my website, so I want to read about best-practices.

Any advice on how to get started would be very welcome :)

I have now created my theme (wohoo!), and thought I should summarize the best resources I found. Lets see..

Resources:

• ThemeTation's three-part guide to create a wordpress-theme from scratch
• Nettuts.com's guide: How to Create a Wordpress Theme from Scratch (And Part 2)
  Didn't actually use this, it's a quite new article, but anyway - it's great. It will get a follow-up in the next few days too..
• Wordpress.org's own guide on templates
  Definatly a must-read for everyone new to wordpress-designing..
• "The loop"
  Essential knowledge, also a must-read
• Directory of all the template tags
  Used by wordpress to actually output blog-content..

Inspiration:

• Smashing Magazine's lists: first, one more, yet another one
• Wordpress.org's theme-directory