Work-Timer is the best tool to easily track your working time. Just press the record button when starting to work and enter a short description when finished. Working breaks and wages can be determined as well.
You can set a timer while working or add entries by hand. Work-Timer is not overloaded with useless features and very easy to use. It also includes the optional Work-Timer Menubar which allows to start recording at any point in time without launching the Work-Timer application. You can process your data further using exports in formats like Excel, CSV and PDF.