This one does not need you to set any breakpoints. It records the entire run. Handy, if you don't know where to start.
Run the program once and after that all the runtime data is available to you. Which means you can jump to any point in the run and verify the code against runtime data.
The user interface is the python code itself viewed inside a Firefox browser. Scroll to a line you're interested in and click the variable.
It requires Firefox and Python 2.5.