I've finished my final year project, which lets you to track your time. it is free and contains absolutely no ads.

There are certainly many apps on the market to do this, but most of that was complicated and require more task just to track your time. my application was designed with Holo design in mind, you guys should love the interface.

If you are interested in trying it out, here is a more detailed description with a screenshot, and links to google play http://play.google.com/store/apps/details?id=com.rheza.officeworld and the website http://www.officeworld.my/

Let me know what you think!