If you’re interested in getting into WordPress theme development and want to create your own themes then you need to visit these sites for their instructions.
CSS-Tricks - A video tutorial on how to convert an already designed HTML and CSS into WordPress
Net Tuts - A how-to guide on creating a WordPress theme from scratch.
Spoon Graphics -Shows you how he took his existing design concept and created a WP theme with it.
Web Designer Wall -A basic tutorial on how to convert a static HTML to a WordPress theme
Line 25 – A walkthrough for intermediate web designers and developers on how to create a WP theme.
Theme Shaper – Create a powerful, up-to-date WordPress theme in 11 individual lessons.
WP Designer -a thorough and easy to understand tutorial on creating a WordPress theme
Theme Tation – a 3 part series on how to create a WP template from scratch
Developer Tutorials -Create a theme from nothing using Photoshop CS3, WordPress, MAMP, Color Schemer Studio, Firefox and Netrenderer.
Eruanna -A very detailed tutorial on how to create a complete WordPress theme from scratch