Here's a great tip that I picked up yesterday that will free up a good chunk of your memory when Maya is running:

Maya, by default, will load the Paint Effects and Dynamics modules into memory... and these aren't small items!!! However, there is a setting in Maya that allows you to tell Maya not to load these modules until they are needed.

You'll find this - not in the Plug-in Manager - but in Window -> Settings/Preferences... -> Preferences. Click on Modules in the list and uncheck both Dynamics and Paint Effects.

The great part is that you dont lose the functionality of either Dynamics or Paint Effects as these modules will be loaded if needed during your Maya session.