Since Windows 7 beta days, I know I could change the logon screen very easily with registry hacks. See HERE.
Now there are easier ways. Our beloved developers made a GUI based Logon screen changer. Since then I change my logon screen whenever I found a cool picture.
Get this little utility (HERE) and change your logon screen to match your style.
Great Tip: You could have same picture for logon screen and your wallpaper and have a unique style experience.
Anand, the Architect 