Google Docs and Google Forms.
Teachers look at the calendar, find open slots and fill out a google form. We get an email with timed receipt for the request and update the calendar. The timed receipt ends any arguments about who booked what first. It is time consuming to keep up with the calendar but with all the lab and laptop bookings we save a lot of grief and provide a more efficient booking experience for our staff.
We are a new google school and when teachers are more adept using google calendar we will move to allow teachers to book thier own times.
Thomas Vaghini
Stafford High School