Here they are:

Calibri

Cambria

Candara

Consolas

Constantia

Corbel

Segoe UI

You can degrade your font choice gracefully using CSS so that if a user is on Vista they will get the new font but if they are not they will get another one.

In this example if the user does not have Corbel they get Lucida Sans. If they don’t have Lucida Sans they will get Verdana and so on.

1

font: 62.5%/1.5 "Candara", "Lucida Sans", Verdana, Tahoma, sans-serif;

With such a limited choice of system fonts this is something for typography fans to cheer about (well a little bit!).