A Free Guestbook

Free multilingual guestbook service with an interface in over 40 languages. You can customize your guestbook with different fonts, colors and images, and choose to enable or disable smileys. Optionally, your visitors can post images with their comments, or use bulletin board codes.

eFreeGuestbooks

Sophisticated highly-customizable guestbook service. Includes private messaging capability, bad word filtering, entry pre-moderation, ip and email banning, the ability to reply to individual postings and more. Optionally, you can remove all advertising from your guestbook for an annual fee.

Guestbook Central

Free guestbook service with customizable colors and fonts.

MyWeb2s Guestbook

Free multilingual guestbook service that supports double-byte character sets such as Chinese and Japanese. Wide range of customization, including colors, fonts and logo. Support for private messages.

Phaistos Free Guestbook Service

Free guestbook service with a wide range of customization options. You have the option to remove all advertising from your guestbook for an annual fee.

UltraGuest

Guestbook service with unlimited entry capacity and up to 3 custom fields. Allows messages to be added privately, and can be completely customized with CSS and a new header. Captcha image verification can be turned on to prevent automated spam. Automatically generates an RSS feed of guestbook entries.

Worth a look if you're willing to pay...