ScheduleOnce

If you have difficulty scheduling meetings with multiple people outside of your company Exchange environment when you can't see everyone's calendar, take a look at ScheduleOnce.  It provides several scheduling options for organizing meetings with multiple people.  One option is to upload your calendar to Google Calendar, and others can see your availability without seeing any of the details of your appointments.  ScheduleOnce is free to try with a few basic features and more advanced features start at $5/month.

http://www.scheduleonce.com/

General Exchange Calendar Schedule