I have been involved in a number of community based projects as well as personal. Here's a list of a few..

Deluge

I maintain the web interface for the popular python based torrent client "Deluge". The UI makes great use of the Ext-JS framework and AJAX to provide a rich user interface approaching as feature rich as the desktop client itself.

fbuploader

fbuploader is written in Python and PyGTK. I started this project after getting frustrated at how the Java based uploader on Facebooks site, (and some of the other, desktop based, uploaders I tried) either crashed the browser or simply crashed.

vmail

I was tasked with improving our email offerings for @UK (my current employer). It was decided to build a solution based around qpsmtpd that allowed a large amount of flexibility. Not being a massive fan of perl I decided to try and have as much of the functionality in a python project, as it would need to be accessed via php as well as perl. This is how vmail was born.

Vmail aims to be as easy to setup as possible, as well as being easy for users to administer their system. Using Roundcube for a web access client and running Dovecot for mail access it allows for a very feature rich system.

pymssql

As at @UK we use MSSQL for our main database and wanting to use Python whenever I can, I occasionally need to connect to the database on linux. My preferred method was using pymssql (which uses FreeTDS). I decided to attempt to add stored procedure support to pymssql, and somewhere along the line decided upon a complete rewrite in Cython. This is still an on-going project however it is nearly feature compariable with the original pure C version.

vsmtpd

Whilst learning all about how a mail system fits together I gained quite an interest in building my own smtpd just to get a better understanding of what is required. Out of this interest vsmtpd was spawned, which is a vsmtpd written in Python leveraging the brilliant gevent library to provide asynchronous sockets that can be used in a blocking fashion thanks to libev & greenlet.