The second tier made up of Ruby, PHP, Perl, Python and SQL. Surprisingly, they now all have roughly the same market share with PHP being the biggest.
The third tier is made up of a number of other languages, which are unfortunately hard to pick off the graph.
Of course, book market share does not directly translate into actual market share for a programming language. As Tim’s article [points](http://radar.oreilly.com/archives/2006/07/state_of_the_computer_book_mar_4.html) out, a number of other factors can influence book market share and year over year growth numbers.