Depends on how much you want to pay but there are two that I like to use both are in different price ranges. Mindbody.com and┬áhttp://www.fitsw.com/. Mindbody was very nice and professionally done – the only downside was that it’s pricey. FitSW seems more tailored for trainers / smaller gyms because its free – just not quite as polished as Mindbody but still very good. Both Fitsw and mindbody have excellent ways to track progress on your client’s fitness and they both do a great job at creating and recording workout plans and diet plans. They both are very helpful in helping me manage all my client’s info in one location.