My iPhone app of choice: Strava Cycling

Ever since my friend introduced this app to me, besides the segments of road where you compete with other Strava users you see your progress each time you ride. How fast you was the ride today?

You get to see simulated Power calculations based on your bike's weight, and track your mileage... Which seems like a lot since I always reset my meter each ride and never actually know how much I cover each week/month.