What I do right now (besides a lots of other things) is implementing a HBV-76/96 version in MATLAB/OCTAVE. I know that there is HBVlight and other assorted MATLAB implementations of HBV around, but I wanted (a) to understand the HBV modeling concepts from scratch and (b) integrate some tweaks on the one hand and apply some simplifications on the other hand. So if you are interested in the sources, feel free to ask…
Andy Philipp's Hydrology Blog 