OS X can be an absolute pain to get MySQL running so when you have finally resorted to using brew to install its, as I have on many occasion there is another pitfall you might face when you try to install other python packages that need to know the MySQL path.
The best and probably most common package that this happens to seems to be MySQL-Python so the following example will be what I use to demo the fix.
Assuming your virtualenv is up and running (or your installing straight on your machine) we need to do the following:
export PATH=$PATH:/usr/local/mysql/bin pip install MySQL-Python
MySQL-Python (or your other MySQL needing package) should now install and you can get back to coding up some awesome websites.