See http://www.astropython.org/resources for a nice up-to-date list of python astronomy resources.
Below is a (no-doubt incomplete) list of cosmology-specific resources I've come across.
CosmoFisher by David Ventimiglia
http://dventimi.github.com/CosmoFisher/
"Python code 'to help create, manipulate, visualize, and gain value from Fisher information matrices'
cosmology module in esutil
http://code.google.com/p/esutil/
Mostly distance measures.
James Schombert's version of Ned Wright's Cosmology Calculator
http://www.astro.ucla.edu/~wright/CC.python
cosmocalc by Tom Aldcroft
http://cxc.harvard.edu/contrib/cosmocalc
Improved version of CC.py with programmatic interface. Not designed for use with numpy.
CosmoPy
http://www.ifa.hawaii.edu/cosmopy/
Interface to the powerful CAMB software for CMB anisotropy calculations.
PyCos
http://www.astro.princeton.edu/~msshin/science/code/index.html
Source not posted.
Andrew Becker's cosmology-1.1.py
http://www.astro.washington.edu/users/becker/python_software.html
OO interface to distance measure calculations.
Taro Sato's Python version of kcorrect by Michael Blanton
http://nomo17k.wordpress.com/2009/08/02/kcorrect-kcorrect-python-port-project/
k correction and photometric redshifts.
Ned Wright's Cosmology Calculator
http://www.astro.ucla.edu/~wright/CosmoCalc.html
CAMB: Code for Anisotropies in the Microwave Background
http://camb.info/
INITIATIVE FOR COSMOLOGY
http://icosmo.org/cgi-bin/Interactive_Step1.cgi
Online and IDL calculator