There is one index at : http://www.tiobe.com/tpci.htm
It isn't much reliable, put still I think it is a bit reliable. Also, you might use number of open source projects at Sourceforge for the given language for giving assumptions, or number of job openings at Monster, i.e. -- Mladen Adamovic http://www.online-utility.org http://www.cheapvps.info http://www.vpsreview.com -- http://mail.python.org/mailman/listinfo/python-list
