Programming Language Usage Graph
by François Labelle
Below is the past usage of top computer languages from Sept 2000 to Feb 2006, as defined by statistics on open-source projects at SourceForge. Granted, this does not necessarily correspond to the "real usage out there" (whatever that means) which I don't know how to get. This is probably the last update to this page as SourceForge no longer provides programming language statistics.
Very different numbers can be obtained by looking at source lines of code in a large software distribution such as RedHat7.1:
Page last updated: October 31, 2010