I was reading an article this morning about how to select a sound card for your laptop if you plan to do pro-sounding recording on the move.
For the most part though, when you say "sound card" in relation to professional sounding recording, what you're really saying is "audio interface," or external sound card. In fact, most interface units aren't "cards" at all, but usually boxes that plug into the laptop either via USB or Firewire (more USB these days).
For the most part, any interface you choose for your laptop would also be great for your regular non-mobile computer. So the questions you ask yourself about mobile recording interfaces are largely the same as you'd ask for your home studio recording interface.
These days, unless you plan to become a commercial recording studio, the interface units for a computer based home studio will be small boxes, i.e. the same as would be appropriate for mobile recording.
So what are the questions you should be asking? According to the article in question, they are:
The cEntrance Mic Port Pro 2 is really the ultimate in portable interfaces. It records very high-quality audio, plugs right into a USB port and has a headphone jack. See my review of it which includes audio samples: $299.99.
The Focusrite Scarlett Solo is small, lightweight, has one combo (mic or line-level) input, and is definitely a great-sounding interface. $109.99.
The M-Audio Fast AIR 192|4 has one XLR/quarter-inch combo jack input and is very portable. $109.99.
Of course there are dozens more out there.