C runs fast and Matlab provides good graphical representation of data. The simplest way is to save data in txt format and create a Matlab script to load and plot the data. A fancier way is to save in binary format. This saves harddisc space. Matlab can handle binary data as well.
for 2D data representing a field value, where you just want to color them according to the values (say density field, pressure field,etc), you can try save them in "pnm" format. google pnm or ppm to see how it works.