Don't know about eclipse, but PhpStorm works fine with CakePHP (and is a great IDE).
You may have to exclude some of the test-cases (because they contain duplicate class definitions) and add PhpDoc here and there to assist code-completion. This probably applies to most other IDE's as well;
For Model-method autocompletion, I add this to the PhpDoc of my controllers
/**
* @property MyModelName $MyModelName
*/
Inside your views, layouts and elements (.ctp), put a PhpDoc block at the start, containing at least this:
/**
* @var View $this
* @var string $title_for_layout
*
* other viewVars can be put here
*/
This way, your IDE will 'understand' that a .ctp file should be considered a 'View' object
For debugging, you may consider XDebug, don't know how good it can be integrated in Eclipse, but here's some examples in PhpStorm, how to set break-points etc.;
http://blog.jetbrains.com/webide/2011/02/zero-configuration-debugging-with-xdebug-and-phpstorm-2-0/
PHPStorm + XDebug Setup Walkthrough