I'm constantly opening an iPython interpreter and having to import my common modules (for me pyfits mostly).
The easiest way to import modules on iPython startup is to look in your
file which is a nice easy way to add python code into your ipython startup (as opposed to the ipythonrc file which is about colours etc.).
In the main function, just add a line such as
This will allow custom code to be run at startup. In this case, iPython loads the pyfits module.
You could add such things as
ip.ex("from pylab import *; x = arange(100); y = sin(x)")
for example if you were working with sine waves a lot.