Well first things first. What will you do mostly with your system? Percentages would be usefull here. EX. 20% games, 30% movies, 30% network television, 20% music.
Also, aesthetics. How do you want it to look. Do you want it as small as possible as not to be a hinderance to traffic, or to be easy on the eyes. Or would you prefer larger speakers and a large subwoofer. You can mix and match certain parts of your system.
What are the room's dimensions, is this a HT dedicated room? If you answer these questions we can certainly get you on the right path.