You can do this using widgets!
If you go to Dashboard > Appearance > Widgets, you'll see a variety of widget options. For your website, you could use an image widget (with an applicable image, maybe your logo?) and then the URL of your website.
You could actually do the same thing for Facebook, actually.
Here's a list of all our widgets:
http://en.support.wordpress.com/widgets/
I hope that helps you!