Kikkoman

Works well. I created a single MobileMe account, and after cleaning up and organizing the my calendars and my wife’s calendars, I was able to get over the air push of Calendar updates to work.

Each person in the household has an iCal Calendar Group to themselves (and more importantly a unique color).

It is possible to just sync calendars, even though you can’t find a screenshot or mention of it on the official site.