I don't see any obvious way to import ICS files into Google Calendar from the API docs here:
http://code.google.com/apis/calendar/developers_guide_protocol.html
And I'd greatly prefer not to have to parse them myself just to send the appointments into GCal. I'm looking for a programmatic solution, not something like import plugins for Thunderbird, Outlook, etc. Third party APIs to do the ICS parsing are acceptable, in any language. Any ideas?
I have created a simple open source .net utility to do just that, available at http://gcalicsimporter.codeplex.com/.
You shouldn't have to parse an ICS just to import it into Google Calendar, it is capable of importing them directly... From the end-user's web view, it's as easy as clicking Import Calendar. From the API, I would look at the Adding New Subscriptions section.
For my iCal2GCal app I'm using the Googlecalendar Ruby Gem to both parse .ics files and then add the events inside to a Googlecalendar. It might give you some ideas on how to go about it. You can check out the full source code.