Although I don't have one myself, I'm very interested in getting myself a bullpup rifle of some sort. If the hideous looks don't throw you off, Steyr's, P90's, L85's etc. all have a really long barrel in a compact size. If, like me - you already have a decent M4 and you want something a little different, do some investigation and see what you like!
You could pick up a G&P AR variant which would be robust externally and give you good reliability and performance. Or pick up some of the TM high cycles.