Excellent source of help for WordPress development. Snippets are a great way to get information on how to complete simple and even complex tasks without having to reinvent the wheel.
Very handy tool to have around
Chris Coyier (from CSS-Tricks) and Jeff Starr (from Perishable Press) are two of my favorite web design bloggers and writers - they have teamed up to write a book on WordPress, which will be online here and this is the blog that goes with it. Awesome!