Also lets not forget the good ol' Utilman trick. It's not as quick as other methods, but it doesn't require any special software or messing about in the registry.
If you've been living under a rock and don't know what I'm talking about, you basically boot into an offline environment and rename the Utilman.exe file to Utilman.something and then copy cmd.exe and rename it to Utilman.exe. Reboot back into Windows and, when you get to the login screen, click on the Ease-of-Access icon and you get a command prompt with full admin privileges. You can now use the "net user" commands to reset the password of the user. When you're done, just delete the 'fake' Utilman.exe and rename the real one back and you're done.