Fabric is a new tool for ssh'ing to many hosts. It has some nice properties, such as lazy execution. You write the description of what is to be done in Python and Fabric takes care of executing it on all the machines you specify. Once you've used it a bunch of times you'll accumulate many "fab files" that you can re-use. You can use it to create large systems too. The API is simple but powerful.
The tutorial gives you a good idea of how it works: http://docs.fabfile.org/en/1.2.2/tutorial.html
It is written using the Paramiko module which is my favorite way to do SSH and SSH-like things from Python.
The Fabric homepage is: http://www.fabfile.org
Thanks to Joseph Kern for this tip!
Know of a similar tool that will cache passwords (such as for sudo)?