The digital music revolution began with a great crash, as music was crunched down into tiny MP3 files that made it easy to share, but reduced the depth and quality of recordings.
At first, it just didn't matter to most people. More songs per gigabyte was the focus. But now that we have bigger hard drives, we don't have to make such a harsh trade off when we want to stick with CD quality or better.
If you're an iTunes user, you can choose to import your CDs in Apple's lossless format, which maintains perfect CD quality while reducing the file size just a little from the original source. Other software commonly uses the more open FLAC format, which does the same thing.
If you want to go above and beyond CD quality, there are now high-resolution or HD music options available. These are delivered at a higher bit rate and higher sample rate, which basically means that these recordings capture much more detail and depth. If you have great speakers or great headphones, and you really care about perfect music reproduction, then check out computeraudiophile.com and hdtracks.com to start exploring the latest in high-fidelity audio.