Here's a short Quicktip about unwrapping in Blender. Although it is not a tutorial about the principles of unwrapping, I hope it helps you to create your UV-maps a bit faster.
I should mention that I used Blender 2.56.6, r33810 from SVN. It could be that older versions don't have this feature. So use the most recent versions of Blender! You'll find recent builds on graphicall.org