1. Requests. The most famous http library written by kenneth reitz.
2. Scrapy. If you are involved in webscraping then this is a must have library for you.
3. wxPython. A gui toolkit for python. I have primarily used it in place of tkinter.
4. Pillow. A friendly fork of PIL (Python Imaging Library).
5. SQLAlchemy. A database library.
6. BeautifulSoup. The xml and html parsing library is very useful for beginners.
7. Twisted. The most important tool for any network application developer.
8. NumPy. It provides some advance math functionalities to python.
9. SciPy. It is a library of algorithms and mathematical tools for python.
10. matplotlib. A numerical plotting library. It is very useful for any data scientist or any data analyzer.
11. Pygame. This library will help you achieve your goal of 2d game development.
12. Pyglet. A 3d animation and game creation engine.
13. pyQT. A GUI toolkit for python.
14. pyGtk. It is the same library in which the famous Bittorrent client is created.
15. Scapy. A packet sniffer and analyzer for python made in python.
16. pywin32. A python library which provides some useful methods and classes for interacting with windows.
17. nltk. Natural Language Toolkit
18. nose. A testing framework for python.
19. SymPy. SymPy can do algebraic evaluation, differentiation, expansion, complex numbers, etc.
20. IPython. It has completion, history, shell capabilities, and a lot more.