[Omega]

Well, I guess it's kind of a matter of what you're going for, and how much time/money you're willing to invest.  You could go for a techy look, or a more artsy look.  That will kind of depend on what your style is.  Also, there's a whole bunch of really cool things that you can do, but that take a lot of skill and time.

Basically, I'd suggest modding it for cooling, color, and a window of some sort.  A 5 1/2" bay fanbus would be pretty cool, but then again, there isn't a massive amount of room for fans.  A front lower intake, a top rear output, and a processor duct would be my main choices.  A glossy black finish is really nice, in my opinion, but that, again, takes a long time with all the recommended steps.  A plexi-glass window on the side of a case can also really add to the appearance of a case when done right.  If your case is extremely crowded and messy, a window won't look very nice.  Remember, you want a window so you can show off your 1337 system, not your mess.  Also, sometimes if you want some extra flash to your system, instead of just a standard rectangualr window, windows integrated into some sort of design can look really really nice.  A light of some sort inside your case can accent a window as well.

Once you make a few decisions about what you're going for, and how much you're willing to invest as far as time and money then it's time to start with more specifics.