site showing booked flights

There are a few sites like this one:

http://flyaow.com/classtandt.htm

They show class availability, but only that which the airlines want you to see. It does not tell you how full a flight is, but does show which fare buckets are sold out and which are still available for sale. So a little careful interpretation of the results can give an indication of how full the flight may be at that point in time.

Note that the number displayed for each class bucket is a minimum number of seats the airline is currently willing to sell in each fare type. For example, a display of K9 means they are willing to sell 9 or more seats in that fare class.