"Time Card" is a simple to use app that helps you keep track of time spent at work. Just check in when you start your work, pause the timer when you take breaks and check out at the end of the day. You can add project names and comments to your entries, as well as manually edit or add entries.
You can compile weekly, monthly or custom reports over your worked time. You can send your time card as a tab separated text file via mail, which you then can import in, for example, Excel. Back up your time card and access the back up file via iTunes file sharing (requires iTunes 9.1 or later).