The relatively recent trend of highly focused, functional, and beautiful apps (February's Haze, for instance) has come produced some wonderful replacements to Apple's proprietary apps. The stock selection on your iPhone is functional, sure, but it could be so much better. And Timeless may just be the timer replacement you're after.
What does it do?
Create multiple, labeled timers that can run concurrently in a tabbed, easy to access row. Or put yourself in stopwatch mode simply by hitting the "play" button in the exact same screen you'd use to open a new timer.
Obviously the main draw here over the timer your phone was born with is the fact that you can set as many of these brightly-colored bad boys as you want. Just swipe left to right to scroll through all your running clocks and set up a new one, and you can even see exactly how many timers you have running at a glance with the icon's notification badge. The clean, bright, interface and large numbers are perfect for those times (such as workouts) when you don't have the patience to fumble with and stare at your screen. You'll be shelling out a buck, but if you use your phone's timer with even the slightest of regularity, it's probably worth it.
The Best: Multiple running timers
The Worst: Only stopwatch uses milliseconds