Actually – lots of stuff. Many resorts have focused on the activities that people like to do in the summer (the type of people who own vacation homes on the mountain)… which pretty much boils down to golf. Many courses have popped up in ski-resort towns for this exact reason. Stowe, VT just added a brand new base resort with an 18 hole course and many other country-club-like amenities… which has helped real estate prices in the fading New England ski-town market. (http://summer.stowe.com/golf/)
If you head to Loon mountain, you can actually rent a mountain bike for the day, ride the lift, and hurl your self down the mountain as fast as you care to go… (which is fun about once a year for the average skier).
Check out what is going on at your local mountain during the off-season!