I have been using
Freshbooks and find it to be very user friendly. I am able to track time with a start/stop timer, generate invoices, track expenses, and run reports. I am able to export reports into an excel spreadsheet. You can upload your logo art to customize what your clients see when they log in to view an invoice or make a payment online through whatever online payment service you use (I use Paypal), giving a very professional appearance.
Freshbooks also provides capability for tracking and coordinating team projects, though I have not yet used this feature.