Found XDebug yesterday, great PHP extension.
Now my custom Reporter class for Simpletest includes code coverage report.
But to make things really look cool, I wrote CodeCoverageRenderer that uses modified version of Geshi. It has only one method – render() and accepts array returned by xdebug_get_code_coverage() in constructor.
Looks like this:

Nice, huh?
Download CodeCoverageRenderer.zip (Geshi w/ PHP support included)