For those who would like a full-featured guestbook that is completely
customizable without having to configure scripts or pay money. I
strongly recommend http://www.getstring.com. For advanced features, it
does require knowledge of html, but there are premade layouts to choose
from.

Nearly everything related to the layout is customizable, and you can
backup and restore your entries amongst tons of other features.

If you are in need of an online guestbook, give it a try, you won't be
dissapointed.