The important thing to know about monitors is that inexpensive consumer listening speakers are generally designed to enhance certain frequencies. If you mix on speakers and/or with an amp that enhances the bass and/or the highs, your recordings will be lacking in those frequencies. That's because you will tend to back those frequencies down with your eq since the speakers are boosting them.
The end-user will play music on many and varied types of speakers, so it has become more or less standard to mix on monitors that are as flat as possible.
Another school of thought is to mix on monitors that act very unlike hi-fi speakers. So rather than flat the monitors look somewhat opposite on a graph -- like the Yamaha NS10. This approach sees a group of people trying to walk in an earthquake and notices the town drunk is the only one walking straight and steady -- What??? yeah I know... just think about it for a minute, it'll come to you (maybe).
Masters of the NS10 turn out very sweet sounding mixes, free of flabby bass and harshness.
There are a lot of good monitors out there, and many aren't any more expensive than a good set of hi-fi speakers at Best Buy.
I like the passive Yorkville YSM1i
http://www.yorkville.com/products.asp?type=33&cat=20&id=119
Everyone has their favorite that they swear by.
It's good idea to test your mix on different monitors, including headphones.
