As mentioned before, some themes (like the Twenty Ten Theme) have footer areas that you can also add Widgets to. You can add to them by first expanding the Widget Area (click the small triangle) and drag the Widgets you want in.

There's another section that I want to quickly talk about - inactive Widgets. If you find that there's a particular widget you've got and you want to keep the settings (for example, you have a 'limited time offer' and you want to add and remove it quickly) you can put it into the 'Inactive Widgets' area. Just drag it in and drag it out as you wish. This admittedly is more helpful when you've got a Widget with more options in it, or something you've written.