SiteRefer

Install SiteRefer in minutes and place ready-made text or graphic links
anywhere, so that visitors are encouraged to tell their friends and colleagues
about your site.

Demo

You
have full control over the appearance and functionality of the installation,
thereby enabling visitors to use an attractive and inviting form. Users may
refer up to five recipients, optionally adding a personal message. You receive
e-mail notifications of all referrals and also have access to a detailed
recommendation report.

Tell A Friend PHP Script

With this PHP Tell A Friend Script you are able to let visitors recommend your
website. Both HTML layout and e-mail layout are template driven and
customizable. Includes several security features to prevent abuse by
spammers.
Demo

Features
include: Processing form data and send it per e-mail; Full customizable website
layout by templates; Full customizable mail content by templates; E-mail message
logging feature; Security features against abuse by spammers. Can only be called
from a site that has been added to a white list of referring sites.

DB Top Sites

DB Top Sites is a Flat File, PHP based script that runs without the use of a
database backend. It features the Top 10 ranked sites, based on ratings, have a
real-time voting system and counts various statistics.

Demo

It
has a basic Admin Control Panel where you can manage users, delete or edit
profiles and validate newly registred users. The script includes email
verification when registering and allows users to vote for their site remotely
and prevents multiple votes for same site. This script is free, only for
personal use.