One of my favorite applications for the Iphone or Ipad is Ifitness by Medical Productions. I currently have version 9.77 on my Ipad.
The applications is very reasonably priced at $1.99 and is available for download through Itunes.
The application opens to a list of all available exercises designated by body groups. For instance on the left is abs, chest, arms, back, cardio, etc. the user simply selects a body groups he or she wishes to work on and there is a large list of exercises the user can do. If you are connected to a network, you can even view videos on how to do these exercises. The user can then log what exercises were accomplished, what the weight was and the reps. And this enters into the users history.
The exercises can also be filters based on the equipment you have available which is great for travel, or by the exact muscle group.
Users can also design their own routine and their own workouts. The history can be exported into a PDF or Excel file for further analysis.
The only drawback with this applications is that it is not all encompassing. There is no calorie intake and calorie burn. It would be great if this application at least interfaced with a food intake application so the user can get an idea of diet and calorie burn.
Also the exercises in the cardio section are limited. I like cross country skiing, which is not an option in cardio. Therefore I had to build that exercise which does not consider how much calories get burned in an average workout.
Still I find this application very beneficial and useful. It is extremely easy to use and really worth the price.