I have a Zoom H4 which someone else has already mentioned. Besides having stereo condenser mics you can attach external mics (XLR or jack). You can use it to record stereo or multi-track 4 tracks at varying quality from MP3 to full CD quality. You can also use it as an interface to record onto a PC (effectively as a microphone recording into Audacity), or simply transfer the sound files to tweak in Audacity.

One thing to bear in mind when recording onto a PC is that if you want to multi-track there can be a timelag between the sound being played back to your headphones, so what you're recording ends up out of synch. You may also find that your PC's fan is louder than you realise!

Personally I think a good standalone recorder such as the Zoom or Edirol is a better investment than trying to beef up your PC, since it is so much more flexible. You can also record well away from that noisy PC fan.