A simple step up in sound quality from your computer involves using a better connection cable from the headphone output. (This goes for the iPod too.) T_bone mentioned a couple, and I have had fun with the Zu Pivot.
Next step up (or skip right to it if you like) is an outboard processor (a DAC). You can get one with a USB input built-in, like the Apogee Mini-DAC, the Benchmark DAC-1, and lots more. You can alternatively use any DAC at all with a S/PDIF input, but in this case you have to buy another cable and another box--a USB converter--to link your DAC to your computer. The Hagerman HagUSB T_bone mentions is one such box, and there are more at different price points. The most upscale one I know of is the Empirical Audio OffRamp.
Personally I use an Apogee Mini-DAC without USB as my main converter. In the office I use an M-Audio Audiophile USB, because it also does analog-to-digital conversion. It is smooth-sounding but a bit short on detail. However it is still a good deal better-sounding than the computer's headphone jack, even with a Zu Pivot.
Next step up (or skip right to it if you like) is an outboard processor (a DAC). You can get one with a USB input built-in, like the Apogee Mini-DAC, the Benchmark DAC-1, and lots more. You can alternatively use any DAC at all with a S/PDIF input, but in this case you have to buy another cable and another box--a USB converter--to link your DAC to your computer. The Hagerman HagUSB T_bone mentions is one such box, and there are more at different price points. The most upscale one I know of is the Empirical Audio OffRamp.
Personally I use an Apogee Mini-DAC without USB as my main converter. In the office I use an M-Audio Audiophile USB, because it also does analog-to-digital conversion. It is smooth-sounding but a bit short on detail. However it is still a good deal better-sounding than the computer's headphone jack, even with a Zu Pivot.