Liftopia.com is not the only online discount lift ticket sales outlet for Colorado ski resorts. LiftTickets.com sells discounted ski passes to many ski resorts around the state.
To find current deals go to http://www.lifttickets.com/ and scroll down to the section where is says 'Find Deals by State'. Click on 'Colorado'
Right now the only deals available are at Ski Cooper and SolVista Basin. Probably more dates will open up after the new year.
Most Colorado ski resorts blackout the major holidays for coupons and special discount passes. Regular season passes should be good to go all season.