Does your script environment have a debugger?

  A question came up at our Seattle scripting meetup about script debugging.
  How does the scripting environment you use, PHP, Python, Perl, Javascript, etc, have debugging features? Can you set breakpoints, follow, go in and out of functions, look up the values of variables, watch variables change as the script is running?
  What other debugging features do you have? What features would you like to have that you don't?
  Obviously you should say what environment you use. :-)