Hi, I'm also a west coaster living in New England. I can't speak for the southern east coast, but 'cross is big up here. Massachusetts has the Gloucester GP, Connecticut has the Providence race, those are probably the two biggest races on this side. You can check out http://www.nepcx.com which has both those races plus 2 more.
I raced Gloucester this past year, it's an amazing course and of course Tim Johnson and Jeremy Powers are both locals gone pro so people are pretty into watching the races. There are a ton of smaller races as well in northern Mass and Southern NH...I did 5 total last year and the courses vary but more and more people seem to be getting into cross so I expect even more to race next year.
There's a New England series that's essentially a pro circuit. Cycle-Smart, Providence, Gloucester. It has amateur races but the point is to be a pro series. They separated from another series due to some UCI BS. That series, while still having high production values, is not a pro circuit.
The MAC is Philly based, roughly. High level UCI stuff combined with big amateur fields. Heavily New England influenced.
MABRA Super 8 is DC based. It's primarily a friends and family series. Great courses but fairly small elite fields and HUGE 3/4 fields.
Sportif Cup are the races that were pared down from the original MABRA series. Grassroots stuff, good courses.
Pretty much up and down the east coast has stuff. In addition to New England, MAC, and MABRA, NJ has some smaller series and a few UCI events annually. NY has a few bigger races. CT has mostly smaller races. NC has a pretty good scene from what I hear too. Lots of opportunities if you are willing to travel a bit.
We have a great series in NC (http://www.nccyclocross.com/). Last year we had 15 races over ten weekends from mid-October to late January. This includes a weekend of UCI races, the NCGP in Hendersonville. There is another smaller series in Asheville (AVLCX) and lots of grassroots races popping up near the coast. Several of us race the MSG series in East Tennessee, which is close by for those of us in western NC. Gravel griders, Roubaix-style gravel road races, and monster CX races are becoming very prominent as well. When you factor in the late summer/early fall training races, you can race CX from late August through January.
Thanks for the response guys. I'm really interested in the best grass-roots, amateur level series out East. MAC sounds like a good start.