Python is my usual go-to language for technical computing, bit Julia is a lot of fun! I'd be curious to hear more from folks who have made use of it in "production" (sort of a tricky label in scientific programmiong) code.
It's a really, really nice language that I find more consistent and easier to grok than MATLAB, but the deciding factor was the lack of the equivalent of MATLB toolboxes with all of their pre-rolled code that made our development as fast as it was.
Edit: I should have mentioned: the Julia add-on packages are multiplying quickly, and are starting to look mature! http://pkg.julialang.org/ I'm looking forward to them overtaking Mathworks on this front too.
I'm curious if it's as sophisticated as Simulink and Mupad, which are completely different programs that happen to be associated to Matlab, or if it's just the image package that we have almost all in Octave already.
Where's the demand? Where is your demand? :-)
There were also some convoluted, non-technical reasons that we went with MATLAB.