Tokbox is a video chat service that allows you to chat with friends over live video. It is browser based app and there is no need to download client software. With Tokbox you can add video chat to your Facebook chat, they have released a Firefox extension to add Tokbox to Facebook chat.
Tokbox also released a Adobe AIR app client that allows you to video chat from your desktop if you prefer that way.
You need to get an account to use the service, once you are in you can call anyone, voice mail or IM. When you click on “call anyone” you will get a message box with unique url, you can send that link to your friends so they can come and talk to you right away. If you prefer you can embed the tokbox widget on your blog or social network profiles so that your users can call you.