You may have noticed that in a SharePoint event list, you can export an event list item as an iCalendar file. Although the link is generated script, you can create this link manually if you want to post it on another page or in an email for convenience. The format of the URL is as follows:
[site name] : This is the address of your Windows SharePoint Services site
[EventID] : This is the ID of the event, which you can get by looking in the URL when you are on the details page for that event.
[ListGUID] : This is the GUID of the list escaped. Yes, I know, this is tricky. The quickest way to get the GUID is to click on the "Modify Columns and Settings" link on the list's page, and the GUID is in the URL. Escaping it simply requires replacing the front bracket with %7b the closing bracket with %7d and the dashes with %2d.
event.ics : You can change the name of the resultant file, but I wouldn't recommend it. The operating system will know that it is an iCalendar file by the extension .ics, so don't change it.