Kill your iPod (part II).
When it comes to audiophiles all is but lost.
With the advent of MP3, the idea of lossless audio seemed to have fallen upon deaf ears. Enter: FLAC, the Free Lossless Audio Codec, it compresses waveforms by finding similarities (like bzip), not by changing the the waveform itself (mp3 et. al.).
When it comes to playing FLAC on a portable, a HD based one is the only way to go because of the increased size of FLAC files -- roughly 1/2 the size of the original uncompressed stream. FLAC players are listed on the FLAC website, but as far as I see it there are only two choices for gapless MP3 and FLAC playback: