Garmin Fit uses location to measure and track you walking, running, or cycling activity, and lets you easily refer back to them or even share them via Garmin's Connect service. It also ties into your music, trying to match a soundtrack to your activity level. Garmin Fit measures: current speed, distance traveled, your route, and your calories burned.
You can also get an optional dongle that uses ultra low-power Garmin Ant+ to wirelessly send data from your iPhone and Garmin Fit to external sensors including heart rate monitors, foot measures, and cycling meters.
Garmin On-Demand takes the traditional turn-by-turn navigation app and lowers almost every barrier of entry imaginable. It's not expensive -- you subscribe to what you need, when you need it, in small chunks for small periods, not massive bills forever. That also speeds up downloads and updates, since only the areas you're traveling need to be transferred to your iPhone. Not driving? Not a problem -- Garmin On-Demand has walkers covered too.
Both apps, as well as Garmin's full suite of apps -- which includes Navigon -- are available now on the iTunes app store.