Short answer: Read up some reviews, look at some speaker sets (or stereos/sound systems if that's your ideal setup), and go try some out in person..
Long answer: Do you want *computer* (magnetic shielded/more geared to fit on a table), speakers or big speakers? Do you want them to go really loud and sound really "awesome", or would you prefer that they produce lots of sounds accurately? Or both? (price goes up!)... Do you mind the separation issues having a *.1 system might produce, is surround sound something you want, are you going for the 'clean' look of all metal or a 'classic' look of black boxes, or perhaps funky looking things like say, itrique (if that's how it's spelt), or klipsch GMX speakers..
As you noted, looks might be important, and really, it all depends, in a lot of cases the computer speaker area gets narrowed down to about a half dozen companies:
*Logitech: Everybody seems to love them, they're the typic store-idealism -- high wattage, very loud and lots of bass.. they tend to look a bit odd at times and don't necessarily have the best sound reproduction, but they all have internal decoder units!
*Klipsch: Bose for people under 30.... both in fitting into budget and.. the whole thing.. you know what I mean (okay just kidding).. Their stuff ranges in all SORTS of price ranges.. You can pick up a set of their cheapest 2.1s for about $100-150, and they go all the way up to $500 or more.. problem is their 5.1 sets don't include decoders and this throws another $100 onto the bottom line, but the sound reproduction is generally thought to be better than that of logitechs..
*Bose: Bose! Good ole Bose.. A little too expensive for most to even consider, but some say it's totally worth it.
*Altec Lansing: Maker of the popular "G5 style" speakers.. to be honest I think they're in between logitech and creative.. some good stuff, but the designs make me wonder how effective they are.
*Harman Kardon/JBL: Great stuff, albeit WEIRD looking -- but the price levels are.. well, it depends entirely on what you want..
*Cambridge soundworks: I think they injected the "home theater style" we all know and love into popularity.. since the mid 90s they've been pushing their subwoofer brick with tiny satellite thing until finally people actually bought it, just not from them.. lol
*Creative: I like to think of them like honda.. The few people that are creative enthusiasts will not buy anything BUT creative. Kinda like us mac zealots

I dunno, some people say their stuff is really great, frankly everything I've ever bought from them fell apart and I was never that impressed with their sound cards either.
*Sony: Addressed for the sake of it.. dunno what to say.
*Everyone else: I'm not an audiophile, myself I chose Klipsch GMX 5.1s because they were... to sum it up, a very good deal at the time I got them, the logitech system that was compared to the klipsch system cost almost $100 more, no it DID cost $100 more, and so I figured what the heck. The only thing I have to say is they're a love/hate thing -- I've mostly heard nothing but good about my speakers, but a few people have called them everything from 'barbaric' to 'not apple' --- like I care. For a $140 pair of speakers, they sound like a $250 pair of speakers, the satellites are *REALLY* sharp and the subwoofer has a very nice range.. plus they actually have decent mids unlike most speakers, so I'm pretty satisfied. I do have them hooked up via optical (there's 3 inputs.. optical, coax, and a 2 channel analog in -- and a button on the controller to switch between the 3), on our g5, and it sounds terrific, but something I found is that G5s can't "adjust volume" with an optical output.. DARN! You can mute though! -- and itunes sound control works *nod*
The other 2 things to be said about this specific klipsch set (does NOT apply to the promedia set, btw -- their documentation differs greatly), are that there's a bit of a background hiss in idle on analog (on digital inputs, they mute when inactive, but you can still detect the white noise when stuff is playing).. it might kill you and it might not, surprisingly the hiss doesn't vary with volume! The other thing is the buttons on the controller for volume control are a bit stiffer than I wish they were, and uh yeah.. *shrug* -- the 5.1 Ultras are a totally different species with dual subwoofer cones and much heavier satellites (and a BASH amplifier, nice thing, though I'm too stupid to explain why!)... so uh.. yeah. *shrug*