TimeTable is a low-cost tool that works with iCal to help you track your hours, so you know exactly how much time you've spent on particular tasks--which can be especially handy for consultants and anyone else who tracks their time for billing purposes.
TimeTable has a simple, multipane interface that plugs right into your iCal data: You see your iCal calendars on the left, which you can select or deselect, and a list of events with date, duration, and title on the right (and you can add a dozen different columns in all, including notes and start and end times). Using a pop-out pane on the left, you can define a date range, and navigation buttons make it easy to jump around through your calendar, and you can toggle through day, week, month, and year views. You can also look at To-Dos in a pop-out pane on the bottom of your main window. A tally in the lower left keeps a live update of total hours, for all events or just ones that you select.
TimeTable can then tabulate and total your hours--which you can quickly export in an e-mail, or as text or CSV--but this app really gets useful when you start setting different billing rates for different calendars. For such a relatively simple and lightweight app, TimeTable can provide a lot of insight into the way you work, and make managing your billing process much easier. The cost of TimeTable has gone up in recent revs, so you'll want to look at more expensive billing apps, too as a comparison--but if your needs are modest and you're already using iCal to track your hours, TimeTable can be a big step forward.