You mean, like, for non-rev travel?
If your airline is a member,
www.flyzed.com gives an indication of whether things look OK, or if they are grim. No load numbers are mentioned though. Contact your Staff Travel department to see if they are a member, in which case they will give you the login ID and password.
Another one that is good is
http://www.amadeus.net. Gives availability information, but once again, no load numbers.
Most airlines consider this proprietary information. A few years ago, a major airline in North America took a Low-Cost Carrier to court accusing them of Corporate Espionage after it was discovered that they had infiltrated their Employee Travel Website and copied load information (I'm talking about thousands of hits from the same source per day).