One way may be to get the Grado battery powered headphone amp. I sometimes run my grado's direct from my Mac G4 laptop, and think it sounds fine. True, not as good as the ipod, and not nearly as good as with the amp, but I wouldn't say it sounds like crap at all. First off, if you're listening to compressed files, then they're going to sound like crap anyway (if we're talking mp3, not losless or something like that). Keep in mind that anything that most peripherals will draw power off your laptop, which will eat away at the battery if you're working away from an outlet (which I assume you are given that you don't want anything that plugs in). If that's the case, then I think there are a number of battery powered headphones amps, and you might want to do some reasearch on headroom, or one of the other forums.
Good Luck
Good Luck