
Most every functional business area has a related professional association that focuses on that function. Almost every industry has a related professional industry association. These two areas are great places to start.
One of the best resources that I have found for identifying professional associations is Weddles Association Directory. It is a great compilation covering associations and societies from Accounting/Finance to Volunteer. If you would like to find an association or networking group by location, a great site to visit is Job Hunt. This site allows you to jump to a particular state, making it easier to zero in on groups that may be of interest. Don't forget virtual groups - Yahoo Groups or Google Groups or LinkedIn Groups.