I compiled some programming language popularity statistics in April 2009, October 2009, October 2010, September 2011 and August 2012 . Here’s an update for February 2013:

I made a number of Google searches of the forms below and summed the results:

"implemented in <language>"
  "written in <language>"

Naturally this is of very limited utility, and the numbers are only useful when comparing relatively within the same search since the number of results Google returns can vary greatly over time.

I’ve divided the table into sections based on large percentage drops from one language to the next.

|------+-----------------+------------+----------+-------+------------|
| Rank | Language        |    # Search| Previous |  Rank | Delta from |
|      |                 |     Results|     Rank | Delta |    Apr '09 |
|------+-----------------+------------+----------+-------+------------|
|    1 | PHP             |  52,699,000|        1 |       |          3 |
|    2 | C               |  39,330,000|        2 |       |         -1 |
|    3 | C++             |  26,490,000|        4 |     1 |            |
|    4 | Python          |  22,410,000|        3 |    -1 |          1 |
|    5 | C#              |  21,474,000|        5 |       |          2 |
|------+-----------------+------------+----------+-------+------------|
|    6 | Perl            |  11,013,000|        8 |     2 |            |
|    7 | Java            |  10,150,000|        6 |    -1 |         -5 |
|    8 | JavaScript      |   7,340,000|        9 |     1 |          1 |
|------+-----------------+------------+----------+-------+------------|
|    9 | Ruby            |   3,456,000|        7 |    -2 |          1 |
|   10 | Lisp Family (1) |   2,955,000|       10 |       |         -2 |
|   11 | FORTRAN         |   2,256,000|       11 |       |        N/A |
|   12 | Lisp            |   1,708,000|       17 |     5 |            |
|   13 | R               |   1,305,000|       21 |     8 |        N/A |
|   14 | Tcl             |   1,072,100|       13 |    -1 |         -1 |
|   15 | Lua             |   1,011,000|       19 |     4 |          5 |
|   16 | ML Family (2)   |     988,400|       16 |       |         -2 |
|   17 | Erlang          |     842,000|       18 |     1 |         -1 |
|   18 | COBOL           |     729,200|       23 |     5 |        N/A |
|   19 | Haskell         |     707,000|       12 |    -7 |         -4 |
|   20 | Common Lisp     |     557,000|       20 |       |         -2 |
|   21 | OCaml           |     528,000|       24 |     3 |         -4 |
|   22 | Prolog          |     521,000|       25 |     3 |         -3 |
|   23 | (S)ML (3)       |     496,800|       27 |     4 |          1 |
|   24 | Scala           |     426,100|       22 |    -2 |          1 |
|   25 | Scheme          |     347,000|       28 |     3 |        -14 |
|   26 | Groovy          |     320,000|       14 |   -12 |        N/A |
|------+-----------------+------------+----------+-------+------------|
|   27 | Smalltalk       |     201,400|       29 |     2 |         -6 |
|   28 | Go              |     201,200|       15 |   -13 |        N/A |
|   29 | CoffeeScript    |     182,800|       31 |     2 |        N/A |
|   30 | Clojure         |     173,100|       30 |       |         -2 |
|   31 | Forth           |     128,800|       26 |    -5 |         -8 |
|   32 | Caml            |     102,600|       34 |     2 |         -6 |
|   33 | Racket          |      93,500|       33 |       |        N/A |
|   34 | Arc             |      76,400|       32 |    -2 |        -12 |
|   35 | Io              |      60,200|       35 |       |         -8 |
|------+-----------------+------------+----------+-------+------------|

(1) combines Lisp, Scheme, Common Lisp, Racket, Arc & Clojure
(2) combines OCaml, (S)ML, Caml
(3) summed separate searches for standard ml, sml & ml