ORIGINAL: AlesisM51
...I would start the thread by stating how much you want to spend...
Absolutely. There are soundcards that have low latency, multiple ins/outs, and high quality to be got for anywhere from $200 to $150,000, for real. Most of the soundcards people discuss on these boards have respectable sound quality for the price range and low latency (as long as you steer clear of USB 1.1-- USB 2 is fine).
That said, here are some of the other things that really make a difference within a given price range:
1. Extra features. Some sound cards have all kinds of cool auxilliary features, such as integrated software-controlled mixers or onboard effects, or built-in limiters on the preamps or insert jacks so you can use an outboard compressor or whatever. These can be a lifesaver if you need them, or a big waste of money if you don't, and may complicate the operation fo the soundcard for the stuff you need to do every day. It's better to buy a soundcard that does the things you need it to do really well, than to pay for a lot of potentially confusing features that you don't need.
2. Number and type of outputs. Extra outputs are a handy thing to have, especially if your soundcard has internal mixing/routing capabilities. The ability to have all your inputs constantly connected to say, a hardware tuner can be surprisingly useful. And as your studio and ambitions grow, the ability to listen to one version of the mix while your singer or whoever hears a different version in her headphones starts to become indispensible. Having more than one set of headphone outputs is also convenient if you want to keep things small and simple. And if you ever want to use hardware effects during mixdown, you pretty much have to have extra outputs.
3. Number and type of inputs/preamps. Most pro and semi-pro soundcards these days seem to come with two mic/instrument preamps and a bunch of line inputs. If you already have preamps that you're happy with, then those built-in preamps are pretty useless, although they don't hurt anything. If you don't have and don't plan to buy additional preamps, then the line inputs are practially useless for most conventional recording applications. But keep in mind that chances are very good that if you stick with this long enough to actually be using 8 or ten inputs simultaneously, you'll probably pick up some specialized outboard preamps. Preamps should include phantom power. Ribbon mics require better-than-average preamps, usually outboard ones with high gain and variable impedance.
4. Portability and swappability. Chances are pretty good that some point down the road, you'll want to record someplace else. With laptops getting better and cheaper every day, buying a soundcard with a simple and easy firewire or USB 2 connection makes a lot of sense, all else being equal.
5. Ease-of-use and "hidden" compatibility issues. When you find a soundcard that looks like it has what you want, run a quick search on the forums and message boards to see what kinds of complaints/issues people are having with it. Some soundcards don't get along with some chipsets, some soundcard drivers seem particularly finicky or buggy, and so on. Every soundcard always has SOMEBODY complaining about something, but what you really want to look out for is long and/or repeated complaints about similar problems from experienced users that don't have a clear fix.
6. Age of the soundcard and upgrades. Soundcards, like everything else in audio, continue to shoot up in quality while dropping in price. At some point in time, you will probably want to replace whatever you get. Higher-quality, specialized cards from well-respected manufacturers such as MOTU, M-Audio, and Apogee tend to hold their "ebay value" quite well, and can often be re-sold two or three years later for close to the original purchase price. "beginner" cards and "do-it-all" cards with lots of bells and whistles tend to lose their value faster as newer models come out with more bells and whistles. In any price range, sound quality tends to hold its value better than extra features do.
As you look for advice, keep in mind that most people have not really used very many soundcards, even experienced or professional users. When people say "I have such-and-such and it's awesome," that may be the only soundcard they've ever used on a day-to-day basis, other than built-in ones that came with a computer. By the same token, magazines and professional reviewers may be able to compare more soundcards, but they probably haven't tested those soundcards on lots of different systems. A soundcard that they fell in love with on their custom-built audio supercomputer may have tons of angry users out there who can't get it to work with HP office machines and so on. So lean towards trusting the magazines/pro reviewers for information on sound quality and features, and check the message boards and online forums for information on reliability and compatibility.
My $.02, anyway.
Cheers.