How do I lock my HTC whenever I want?

I have a HTC Wildfire S and set up the screen lock pattern for it. This triggers after some time but sometimes I want to lock it myself, for example if I leave the office and let my phone on the desk. In **Settings | Security | Lock phone after** I can use the "Immediately" option but this closes every time the screen turns of. Is there some way I can keep it to lock after some time as it is now but also lock it whenever I want?