Those clever kids at www.demonsters.com have written a fantastic Debugger for Flash.
Flex user need not read on really, you have one of the these already. Demonsterdebugger is for those of us still using use Trace() statements rather than bother with Flash's awkward built-in debugger console. Demonsterdebugger might just see the end of my close friend trace();
demonsterdebugger is an AIR application that does just what it says. Allows you to inspect the classes of a swf file at runtime. Properties and methods can be fiddled with and change while the swf is running.
It features a purposefully simple design and nifty frame rate and memory monitors.
check out this tutorial to get up and running in 2 minutes flat.