Ok after taking a quick glance at the software I am assuming you are doing Acoustical Audio Analysis and not electrical. In that case, and because I was blind before and missed you saying USB, you can go with cheaper than the RME. RME still has some PCMCIA and Expresscard Solutions, but they don't deal in USB usually.
My choice would probably be this for quality of interface....http://www.sweetwater.com/store/detail/USBPre/
Sound Devices you might or might not know, depending on how much work you do with field audio. They are well known for their field recorders(Not quite Nagra, but definitely a close second). This is a fairly new device for them, but I would expect good things out of them.
If you want something cheaper that will work however, you can certainly go that route. Things like this...http://www.sweetwater.com/store/detail/FastTrackPro/
Will serve you fine most likely.
Sorry I can't give you any first hand experience on them, I use the FW side of things as I deal with audio primarily and I prefer the FW interfaces. However these should serve the purpose you are looking for. Also feel free to look at PCMCIA interfaces, or Expresscard, as you can find some good ones in there. RME carries both PCMCIA and Expresscard for example, and you can find a fair variety of other stuff as well.