I've just created a calendar of photographic exhibitions in London that can be syndicated into various diary tools such as Google Calendar, iCal, various feed readers, and your own websites.
An example of content is at http://www.phase.org/pages/photoExhibitionCalendar/
If you already have a google calendar, you can add it at http://www.google.com/calendar/render?cid=j518lhj8ogdhus3ieh0ktminao%40group.calendar.google.com
The iCal-format feed is at http://www.google.com/calendar/ical/j518lhj8ogdhus3ieh0ktminao%40group.calendar.google.com/public/basic.ics
The XML feed is http://www.google.com/calendar/feeds/j518lhj8ogdhus3ieh0ktminao%40group.calendar.google.com/public/basic
This is syndicated at londonphotoexpo
The calendar is by no means complete. To add to it, please email me.