well the "best possible" could extend into the thousands or tens of thousands easily. i dont think this is what you meant though.
give us a budget and a few ideas on what you want to use this system for, room size to use it in, and what you need to connect it up to. are you looking for pc speakers? htib? receiver+speaker+sub handpicked solutions?
going out to a pcshop for pc speakers, audio store for the others (or best buy, other such retailer) can get you a good idea how speakers sound.
personally i absolutely love my setup. 5.0 Klipsch Quintet IV, Klipsch 450w sub, Pioneer vsx-30 receiver. cost me a bit over USD$1300 though. they make add on speakers for 7.1
before that set i used to use a 5.1 logitech set i bought for around $120 which sounded good for being pc speakers. good enough to keep me happy when cranked but when you compare them to true home theatre speakers they pale in comparison.