Add-ons, what are they? Well...they can be a lot of things. Search Engines, Virtual Postcards, integrated email and more.

I'll start with virtual cards. Why? Because I am the webmaster for Cybergreet.Net and if I want to keep my job, I better give them a plug. Seriously though, virtual cards help to enchance your site and give your visitors a reason to come back. Additionally, they introduce your site to new potential visitors and or customers.
Cybergreet Virtual Postcard Hosting
More Virtual Card Hosts:

• Hyper-CGI.Com - Fast, easy, advanced postcard hosting. They offer nifty features like a custom subject and a one line add-in to the email sent to recipients.
• SuperSportBike.Com - They host cards for Motorcycle Sites
• AllBirds Card Hosting - If you have a birdsite, they are the folks for you. They only host "birdcards".

Banner Exchanges - A banner exchange is exactly what is says. You show some banners on your site and your banner appears on another site. The ratio is normally 2:1, meaning for every two banners you show, your banner appears once. Since these exchanges are free, that is a pretty good way to get your site viewed by a wide audience.

• bCentral - Microsoft's Free Banner Network. It used to be called the Link Exchange until the big guys bought it. They have kept the functionality and added a ton of new services to it.
• Exchange-it - Another good banner exchange. Site content must be acceptable to children.
• Micro-Find - A small banner exchange open to Virtual Postcard, Screensaver and graphics sites.
• SuperSportBike Motorcycle Banner Exchange - Another small exchange site. For motorcycle sites only.