In reply to Dave: Jackson Hole is probably the hardest core of the US resorts mainly because it has a cable car, but still quite tame (compared to Europe). I really liked Alta which someone else has mentioned, mostly because of the amazing quality of the powder. Telluride is good too. For a quirky small and very friendly resort, Monarch is worth a visit, and had the best snow in Colorado I thought.
The worst thing about the US though is the chairlifts without foot rests, kills your knees! (assuming thats still the case as I havent been for a good few years)