Here's a little handy tip I discovered today thanks to the Apple Quick Tip of the Week podcast:

You can use Spotlight as a basic calculator.

Now the the thing is, the Dashboard widget is fine and all, but this is so much simpler and faster for doing quick math. And the other cool thing is that if you press Return, the calculator application will open up if you need to do something more advanced.

The episode I found this in ("Tip 44: Do More Than Search") also shows how you can use Spotlight to look up a definition of a word, but I think that one is kind of obvious. Of course, I'm probably one of the few people left who didn't know about the calculator thing, but whatev'.

So, here's how it works:

  1. Open Spotlight in the usual manner (either by clicking the Spotlight icon on the right side of the menu bar or by pressing Command-Space).
  2. Now, type out a simple calculation like, say, this: 6*7

And you should see something like this:

Pretty neat-o, huh?