I wrote up a small addon that outputs the following data:
- Number of members of each class
- Highest level of each class
- Average level of each class
The mouseover the "Number" wiill show a breakdown of level ranges for each class. The output of this is configurable in that you can set the start (19), range (10), max level (60) and sorting. This makes it scale well without (hopefully) any coding changes and gives you flexibility to say, show a breakdown of every 5 levels starting at level 30. It can be pretty obscure as well, e.g: Level breakdown every 2 levels starting at level 10.
Example can be found at:
http://grunts.roster.vgjunkie.com/addon.php?roster_addon_name=numbers
It can be downloaded by going to http://www.wowroster.net/Downloads/details/id=61.html