I've just recently gotten into http://zwift.com/, it's the only thing I've found that makes riding indoors tollerable, almost fun. The power meter on the bike connects to zwift, the more power you put out, the faster you go. There are a few virtual locations you can ride around, ride with other people. There are also workouts, where you need to hold a certain power for certain time. The workouts are scaled based on the power you can do. I prefer working out with power than heart rate since it responds a lot faster and is less affected by other things going on in your life. Mind you, a bike, a trainer and a power meter is pretty expensive if you don't already have them.