If you want to hear every detail in your music--every breath, every strum, every rattle--lossless music formats are the only way to go. But if you hate the idea of your precious music files being tied up in some corporation's proprietary format (i.e. Apple Lossless and Windows Media Audio Lossless), the most popular choice out there is FLAC.
You can find free programs for Mac, Windows, and Linux that will play and rip FLAC files, but finding a FLAC-compatible MP3 player isn't quite as easy.
I've rounded-up my favorite FLAC-compatible players into two groups: MP3 players with FLAC and Portable Video Players with FLAC. The distinction is really just a formality to keep our comparison charts from busting apart, so definitely give both roundups a look.
It's also worth mentioning that if you own an older iPod and you don't mind tinkering with it, the open-source Rockbox firmware lets you add FLAC audio playback, custom EQ, games, and tons of little surprises.
Have some wisdom to share on why you think people should make the switch to FLAC? Share your experience in the comments section.