Aspiring WordPress theme designers should take a look at this Developer Toolkit by iThemes. It’s not so much a downloadble kit as it is a tutorial page containing links to helpful tools in creating a WordPress theme. But there are some tools and tips that were overlooked:

Firebug for Firefox

Although mentioned in one of the links, I find Firebug more convenient than the Web Developer Toolbar. It’s a Firefox add-on, but a Lite version can be used for other browsers.

Aardvark for Firefox

Another Firefox extension, Aardvark lets you inspect elements simply by hovering over them.

Developer Toolbar for Internet Explorer

It’s easier to debug in Internet Explorer with its own IE Developer Toolbar. It’s only compatible with IE7, but it’s better than nothing.

IE8?

Should we start testing themes in Internet Explorer 8? The first beta has been released, and it’s shipping in standards-compliant mode by default. More importantly, it automatically comes with a Developer Tools feature that looks a lot like Firebug, which makes debugging your themes easier.

Other Browsers

Don’t forget other browsers! Test your theme in Safari, Opera (Web Developer Toolbar available), and other browsers.

Admin Theme Preview for WordPress

Ordinary theme switchers let other people see the changes you’ve made to your website when you’re testing out a new theme. But Admin Theme Preview is a plugin that only lets admin users see those changes. See also: Preview Theme and Theme Test Drive.

Submit Your Theme!

Let other people know about the theme you’ve created by submitted to WP theme websites like Free WordPress Themes.