You might want to check out Premember
It's a desktop tool with the following functions:
-Time tracker (one click start and stop)
-Customizable Invoicing (will be added in the near future)
-Calendar that can be customized
-Import and export to and from Outlook will be added soon
-A tool to look back in time which shows you what you were working on, even if you forgot to track it manually.
It's currently free because it's in the beta stage, so if you request certain features, they will have a good chance of ending up in the final product.