Simple and large, quite often the key to a perfect app. Nano Timer Plus is both. It simply displays a countdown timer in minutes until the last minute, when it displays seconds. The outer circle counts down the seconds within each minute, starting in green, changing to yellow with a few minutes remaining and finally changes to red as time is running out.
A great companion app if you're making a presentation, teaching a class or measuring a time-out moment. There's a free (I love free) version, but I opted for the $0.99 version for its extra features.