I have a Mac too, and use two programs:
1. Ascent - don't even think about it, best $35 or so you will spend! It is fantastic. I've been using it for years.
2. TrainingPeaks.com: This year I decided to keep track of all my other workouts (mostly climbing and yoga) plus weight, sleep, stress, etc. TrainingPeaks allows you to easily download the cycling stuff, and add other workouts, etc. I don't like the way it handles cycling as much as Ascent, but it is giving me a very good overview of my whole fitness profile. Web-based (Firefox)