Here is WordPress Theme Generator – a free online service that let you to create custom themes by keying in few inputs like layout, body size, number of side bars, position of side bars, colour schemes, etc; then click a button to download your customised WordPress theme as a zip file to your desktop.
The coolest features of WordPress Theme Generator is its ability to show real time preview of the theme. As you configure the various element of the theme you can see the live preview on the right side section of the window.
For non-programmers this is a great service to create custom themes. Even if you are a programmer, you can use this service to create a base theme with just few inputs. This service definitely saves lot of development time.