I agree with the suggestion about skimoguls. I have worked with them for over 4 years - 2 as the president of the NCSU ski club, and was very happy with the trips they put together.
For eastern trips, take a look at www.snosearch.com
. They put together soe great trips to Vermont (Killington and Sugarbush), Maine (Sugarloafand Sunday River), and Quebec (Tremblant and Mont-Sainte-Anne).
Both of these companies also have great perks, i.e. free trips for group leaders is you get enough people to go.