Stop in to a local music store such as Sam Ash or Guitar Center or any other one (including the online stores) which has a "pro audio" department. Tell them you're doing research on what interface you need. Get opinions and pick their brain, as some of them are fairly knowledgeable .... and some are not, so you need to determine if they are shooting straight or blowing smoke. Tell them your needs and budget and that you want a reliable interface for your studio.
You don't want to buy a combo interface....and don't buy one of the interfaces with a midi cord attached (these are the cheap ones and give a lot of trouble) .....stay away from the gimmick interfaces and if the salesman is trying to steer you into buying one of them, thank him and leave....... none of the mixer plus an interface or a guitar processor plus and interface..... buy a simple straight up USB external audio or audio/midi interface. We get requests here periodically for help with those gimmick interface/mixer/guitar processor things and it's not too often I recall them getting it to work like it should..... avoid them like the plague.
M-Audio, Presonus, Focusrite, Roland are some of the ones that we recommend here the most. Look at this site....
www.beaglesound.com ...it's from another cakewalker who took the time to put together a listing of the more popular interfaces.
Remember that when you buy one, you want to get the best that you can afford to buy. It is and will be the heart of your recording studio for years to come.
Depending on what you buy, I have seen the audio only interfaces starting for around $100 going up to about $300 for the 2 channel interfaces, and rising above that to $1000+ for the multichannel interfaces. The interface I bought was $300 at the time and has now been replaced by Focusrite with newer models, however, it works as flawlessly now as it did the day I bought it and got it set up for my system. Not a bit of regret on my part for paying that price for it. At the time $300 was a ton of money, but worth every dime.