What's the best place to store and load static data for plugins?
What format is the source data in?  If it's already in a multidimensional PHP array, then it might be as simple as having a data.php file in your plugin and doing a require_once in your plugin's init() method and you're good to go.

Even if it's in a different format, loading it from init() and parsing it into the multidimensional array is a good option.