I vote for python. You might have to look a little harder if you want job specifically as a python programmer, but if you were picking a language just for resume padding, you wouldn't be picking c++ either, you'd be picking more java or some .net. The reason I vote for python is that it's further from what you've done so far. You've got decent coverage of the compiled language area already but there are concepts in scripting languages that you just don't learn to think about with compiled languages (python isn't really that far out there as far as scripting languages go though, ruby and javascript are more interesting). It might change the way you think about programming in other languages but if it doesn't, you've at least covered the area and learned that it's not your style.
The great thing about python is that it's really friggin' handy. I taught myself what I know of it now by using it to parse log files and other various little things that were handy to automate. The interactive interpreter is really nice for learning/debugging/prototyping. I use it to do stuff in my day-to-day work that I never would have considered bothering to try in java.
A couple of counter-points to Dhaval00's post:
1. Youtube is largely implemented in python. It's also in wide usage elsewhere in google. Some of the more adventurous 'enterprise applications' definitely go outside of the compiled sphere (although of course you can compile python).
2. Python 3k will break backwards compatibility, but if you're looking for a job a) there will be 2.x codebases in use forever and b) all your knowledge will be transferable, the only 'breakage' is a few nits that are easily explained and it's even largely possible to automate the translation of source code.
3. Scripting languages can be picked up easily but that doesn't mean they are devoid of interesting, useful concepts. Generally speaking, they have way more interesting, useful concepts than compiled languages, that's why they exist (it isn't because they execute faster! 😉)
I'm just playing devil's advocate here to the pro c++ posts. If I could only learn one, I'd probably do python, but in reality I might opt for the c++ course and teach myself python on the side.