I program mostly in C and C++ (although I prefer the style of C).

For complicated (but non-intensive) mathematical calculations, I often use Mathematica, where the natural-style input and the functional style make it easy to hack things together without thinking too much about the fiddly technicalities of program design.

For postprocessing data and visualising it, I use gnuplot and Matlab (the latter apologetically).

I sometimes use PHP for making simple web applications, but more often I use it as a shell-scripting language. I have never got on with bash, awk or sed and find their terse syntax unhelpful.