matplotlib
matplotlib is a python 2D plotting library which produces publication quality figures in a variety of hardcopy formats and interactive environments across platforms.
Project Source: https://github.com/matplotlib/matplotlib
Project Homepage: http://matplotlib.org/

vincent
Python to vega translator, built for making visualizations with D3.js.
Project Source: https://github.com/wrobstory/vincent
Project Documentation: https://vincent.readthedocs.org/en/latest/

d3py
A plottling library for python, based on D3.
Project Source: https://github.com/mikedewar/d3py

seaborn
Seaborn is a Python visualization library based on matplotlib. It provides a high-level interface for drawing attractive statistical graphics.
Project Source: https://github.com/mwaskom/seaborn
Project Homepage: http://stanford.edu/~mwaskom/software/seaborn/

prettyplotlib
Python matplotlib-enhancer library which painlessly creates beautiful default matplotlib plots.
Project Source: https://github.com/olgabot/prettyplotlib
Project Homepage: http://olgabot.github.io/prettyplotlib/

pygal
pygal is a dynamic SVG charting library written in python.
Project Source: https://github.com/Kozea/pygal
Project Documentation: http://pygal.org/