144blocks - Colorful way to track your time! Inspired by Wait But Why
Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.
Clock mini - Simple clock app in the Dock
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
World Clock iOS 8 Widget - Check the time, anytime. Just pull down Notification Center.
RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.