Hi! I had the same concern--what are good monitors? Everyone told me (at the time) that JBLs are great, blah blah, but get Yamaha NS-10's because all the big studios have them.
Then I found a great article in Recording magazine. In sum: Go to the store(s) you'll likely find pro monitors, or the best stereo retailer in town if there aren't pro audio shops near you. Take three CD's. One should have fat, punchy bass, like a hip hop CD, or Herbie Hancock, whatever. The second should be classical music, mastered within the last 10 or 15 years. And the third should be simply your favorite CD, the one you know inside and out.
First, ask the salesman to cut out all EQ or other effects which make home audio consumers say "ooh", and start the "bass-test" CD. The bass should be clean and clear, not heavy and muddy. Heavy and muddy means there is significant coloration in the speakers or simply lousy bass replication, which will result in your mixing the bass improperly. Some small monitors have virtually no bass replication. Next, switch to the classical CD, and listen with your eyes closed. Do the strings sounds like keyboard patches, or do they sound live? Can you hear the scratch of the bows? Can you feel the basses, or are they indistinguishable from the cellos? What about the winds? Can you hear *each and every wind player simultaneously*? Are the timpani clean and resonant? If the monitors are good, you should hear the complete range of the instrumentation, well, completely. *It should sound live*. (The logic behind the "classical test" is that, while we may never know exactly what an electric bass or synth patch should sound like, we do know what a violin or an oboe sounds like. If these instruments are replicated well, then our electronic ones will be as accurate as possible too.) Finally, put in your favorite CD. Let 'er rip!! Is it smokin'? Is that vocalist oh-so-clear? Is the high-hat crispy and the bass mean? Did you hear something you never heard on your old monitors, a little mistake, perhaps, or a secondary bass line that you didn't hear floating around there before?
If the monitors pass these three tests, they're the ones to get. I myself took
Tannoy NFM 8's (a few years ago, still lovin' them), but they're about a grand a pair. And, I can tell you from experience that Yamaha NS-10's really are used in pro studios for near field monitoring. Even though the Yamahas sound kinda weak, the theory is that they replicate the quality and range of low-to-mid-priced consumer radios and stereos. So if you can get a good, balanced mix on the Yamahas, it will sound good just about anywhere. It's a fairly effective theory, actually. Just bear in mind that the NS-10's have a weak bass and a fair-to-middling dynamic range. So if you mix with them, be careful not to overcompensate by pushing the bass levels too high on the mixer.
Okay, I wrote a mouthful, but I do hope it's helpful. I believe monitors define the mix, and should be chosen as carefully as a $2000 sampler or $5000 saxophone. Good luck, and happy hunting!