One place, if you have the time or interest, is to look at the Non-Profits form 990. These are required to be filed yearly and provide a great deal of detail on some interesting elements like salaries of key people.
One place to look at this information is on the National Center for Charitable Statistics.
Here is their website nccsweb.urban.org
I always ask the person that calls from the firefighters or police associations what it is like to be a cop or a firefighter. More often than not, the person on the other line either hangs up or explains timidly that they are "working on behalf of" those organizations.