put a fan hole at the back for each comp, window in the side of any shape you want, LED strips round the front through opaque acrylic may work well. You could make the edge curved to give a bit of a different look, use different colours, casters, build it into something else such as into a wardrobe etc. Also , something that bugs me allot is the way the graphics card power cables stick out, you could make encasements for these - would improve the looks and the cooling efficiency.
Just a question but how thick is the acrylic, colours your planning to use etc. as people will be able to refine really well if you have more information on this... good luck!