Since we are currently on the topic of web development, developers who use Internet Explorer should definitely check out the Internet Explorer Developer Toolbar.

This IE plugin (currently version beta 3) offers many features desirable to developers, including:

• Source syntax highlighting.
• Element style information.
• HTML and CSS validation.
• Easy disable/enable IE options and cache information.
• Outline tables and cells.
• Much, much more.

This handy tool works with IE6 or 7 and is completely free.