Webmaster
Tools
Garage

Free Web Tools for Developers

RecommendIt	The oldest service of this type. You can specify return URL and the text of the message. You can use a simple link or a form.
ReferMe	Visitors do not need to leave the site to recommend it. You paste the HTML for the form into your pages. You can completely customize the message that is being sent. Thank you pages asks if they want to recommend it to some other people.
LetEmKnow	Recommendation form can contain any number of fields, you can specify return URL.
CGISpy (Site Recommending)	With send a site, people can fill out a simple form, and email your site to a friend. It helps you build traffic to your site.