SCCA:
http://www.wdcr-scca.org/events/autocross Great location and fast courses, but alot of classes and strict. I personally have not run with this group.
BMW NCC:
http://www.nccbmwcca.org/content.php?117-autocross I havent run with this group, but many of our members do. I've heard nothing but good things.
Capital Driving Club:
http://capitaldrivingclub.com/ This is who I run with, really laid back, multiple locations (not always a good thing) LOTS of events (two a month). No classes, but you get time added to your raw time based on tires,weight,HP.
There are more around but these are the main 3 that I am familiar with