A few useful packages:
requests - the quintessential library for making http requests of all kinds. The standard library has urllib but requests is much nicer.
boltons - various decorators and utilities that are useful. Some of them are advanced, so they may not be immediately useful to you.
pyglet - a library for game development, includes a publish / subscribe pattern, keyboard hooks, basic sound playback, advanced visual stuff through open GL, etc. If your making audio games and actually want to learn how libraries like AGK and AGK3 do things behind the scenes, you'll probably want this.
pygame - It's similar to pyglet, but I haven't personally used it much so I can't really recommend it; I'm just including it here for completeness of packages you might be interested in.
libaudioverse - an advanced audio library. Coded in c++, but with python bindings, so it's on pypi. Again, if you want to really understand and have full control over audio in games you might make, use this.
twisted - a full-featured networking library. If you need to write a server, a client, a proxy, etc, this is something worth considering. You can use 'socket', which is low-level and from the standard library, but twisted is nicer.
sqlalchemy - an awesome database toolkit. If you need an app to use a database, this is my personal favorite for the job. It has an orm, an object relational mapper, which maps python classes to database tables. A specific class you code represents a table in a database, and an instance of that class represents one row in that db table. In this way you can really easily define a database schema just by defining what a class looks like. I use it all the time in web applications, my game, mud bots, etc. It also supports a bunch of different databases so you can use sqlite when testing locally, and mysql or postgresql when testing on the server and running your app in production.
geocoder - a package to get coordinates from an address or city, or a general location from an IP address.
mbf - Just gonna throw this in. It's a library I wrote for making mud bots. It isn't on pypi yet (one of these days I'll put it up), but it is on my git hub. It still needs some polishing up, but you can define triggers (with regular expressions of course, or not if your lame), timers (using an interval or at a specific time), and it handles connecting and logging into a mud, as long as you provide a few pieces of information. In the future I'll update it so you can register multiple bots on one framework object, as well as giving it the ability to proxy your mud connections (so you can connect to a server running mbf and play as normal, while bots are controlled from your server).
click - If you need to make a command-line program or script that takes more than 1 or 2 options, click lets you easily define what options and arguments you want. If your program is more complex and needs subcommands (think git commit - where commit is a subcommand of git), that's pretty easy to do as well.
wx - If you need to make accesible UIs, wx is pretty much the standard.
cryptography - If you find yourself needing to do light or serious crypto stuff, the cryptography library most likely has what you want.
These were just the ones I could think of off the top of my head. There are a lot more out there, and if one doesn't do quite what you want, you can always make your own.