As you know, Spanning Salesforce has feeds that contain your calendar events from salesforce.com. But until Ray Ozzie's vision of RSS+SSE+hCalendar gains widespread adoption—which, given the fact that Microsoft is only now adding .ics support to Outlook 2007, doesn't look like it's going to happen any time soon—you're going to need something a little less "Web 2.0ey", which is where the newest Spanning Salesforce "feed" comes in:
Note that this isn't an RSS feed—it's an old-school published .ics calendar, albeit a dynamically-generated, personalized, encrypted, salesforce.com-integrated one. You must be a Spanning Salesforce user to access it, but signing up for a free 30-day trial takes less than a minute. When prompted by your calendaring app to log in, just enter your salesforce.com username and password.
The service is currently in beta, since it's only been tested with Apple iCal, but results with that application have been great. If you use another iCalendar-capable calendar app, I'd appreciate it if you tried it out and gave me some feedback.
I'll be posting more on this in the coming days, since there's some pretty cool RSS+SLE stuff going on under the covers. Thanks to Ismael Ghalimi for the impetus.