Dreamweaver CS5 is very useful to design or modify a Wordpress theme. It inspects CSS elements in Live view (after seting up a test server), but its unable to trace original wordpress code responsible for generating front-end HTML. So, I'm looking for a smart dev tool which could trace internal PHP code responsible for generating selected front-end HTML.
Any decent IDE for PHP comes with search capabilities. It is usually rather easy to find code responsible if it uses specific ids and/or class names.
Personally I use NetBeans for PHP, also see Software for WordPress Theme and Plugin Development? question. A tons of good tools mentioned there.
Any IDE with a built in debugger would be useful to you. I use http://www.jetbrains.com/phpstorm/ . It's very simple to setup with a debugger.
There are IDEs out there that requires you to add a debugger as a module and you spend most of your time making the module work instead of debugging your own code. That's why I suggest something as simple as PHPStorm.