NPR, source of all good things ever, has released a quiz to allow us to test our ears' ability to recognize high quality audio files (uncompressed .wav files) to their lower-quality mp3 brothers and sisters. Check it out here:
Fortunately, the quiz (which takes about 10 minutes, max) will reorganize itself each time you retake it, so you won't recognize patterns in the answers. This allows you to take the quiz several times to not only check your accuracy but also your consistency.
Hint: Listen for dead space in the songs to hear what's going on (nothing, if the quality is good). And compare the way hard sounds, like "s" and "k" or "ck" are heard.
How many of the 6 answers did you get right? I got 4 on my first try (with 1 lucky guess), but only 2 on my next try. It's a lot harder than I thought, and I fancy myself a pretty good listener....