If you don't have a powermeter, the HRM is decent. Check out "TRIMPS" score on Golden Cheetah - if you have a Garmin that downloads HR data, it'll calculate the time spent in each HR zone and give you a total "TRIMPS" number that represented the weighted composite of it.

TrainerRoad is really good as well - if you're going to train seriously indoors (sounds like you are), you really have to at least try it for a month. Even if the virtualpower isn't powermeter-accurate, it doesn't matter for indoor training, since it's the relative efforts to your tested FTP that matters, so you'll still be getting killer good workouts at exactly the right effort ranges as long as you're basing your training off a FTP test. (There are ready-to-go FTP test 'workouts' on TR.)