Dig Deep Fitness is the best iPhone fitness application because it is the only iPhone fitness application that was developed by a weight lifter for other weight lifters.
Currently in an early Beta, Dig Deep Fitness allows users to create an exercise library, go through workouts, and record weights, reps, and any exercise notes.
Soon, Dig Deep Fitness will have a webtop version for in depth usage including program design, reporting, and message board.
In order to help users maintain motivation, recent exercise performance records are displayed at the bottom of each exercise screen.
When selecting the next exercise in a given workout, users can either create a new exercise or choose from a list of existing exercises. Any newly created exercises immediately become part of the user's library.
I just bought an iPhone and this is exactly the kind of app I was looking for. I can't wait to start using it.