MOTU offers excellent, professional quality USB and firewire solutions. They're high end but thought I'd mention it since you're looking to improve. You didn't say by how much.
In particular, a really great interface for mobile is the Traveler-mk3. It can be bus powered directly from the laptop. It works great on desktops and as a stand-alone mixer too. Doesn't particularly need any pc.
This suggestion is only if you're really serious about audio, though. Otherwise, there are less costly solutions available. http://www.motu.com/products/motuaudio