You can install each extension individually, or you can link the extension directories into your IPython directories (what I do):

ln -s $(pwd)/extensions $(ipython locate)/extensions
ln -s $(pwd)/nbextensions $(ipython locate)/nbextensions

Add a gist button to the notebook toolbar:

$ curl -L https://rawgithub.com/minrk/ipython_extensions/master/nbextensions/gist.js > $(ipython locate)/nbextensions/gist.js

and load it by adding to your custom.js, found in $(ipython locate profile)/static/custom/custom.js:

IPython.load_extensions('gist');

Enable 2x display of matplotlib figures (no longer necessary on IPython master)

install the extension:

%install_ext https://rawgithub.com/minrk/ipython_extensions/master/extensions/retina.py

load the extension:

%load_ext retina

Generates floating table of contents inside your notebook from the heading cells. Adds a button to the toolbar to toggle the floating table of contents.

install the extension:

$ curl -L https://rawgithub.com/minrk/ipython_extensions/master/nbextensions/toc.js > $(ipython locate)/nbextensions/toc.js
$ curl -L https://rawgithub.com/minrk/ipython_extensions/master/nbextensions/toc.css > $(ipython locate)/nbextensions/toc.css

and load it with this in your custom.js:

IPython.load_extensions('toc');