Every month, TIOBE Software publishes its TIOBE Programming Community Index, a measure of programming language popularity based on a variety of sources. The current list, TIOBE Programming Community Index for July 2009 lists MATLAB as entering the Top 20 list (for the first time, I believe). While no such ordering is likely to be perfect, TIOBE seems to be one of the more comprehensive efforts for this sort of thing.
I encourage readers to visit the TIOBE site because it is interesting to know what other tools are available, and what new languages are emerging. For interested parties, the July, 2009 Top 20 are, in descending order of popularity:
5. (Visual) Basic
14. RPG (OS/400)