The Yamaha HS Series has gotten great reviews by lots of people. I know of some people that use
the HS-80M and put out some really good mixes. Another good option is the older KRK V series (Not VXT, those are the newer revision and would fall out of your price range). the V series is out of production and you would have to buy them used. I know several people using either the V4, V6, or V8s that also put out quality work. Maybe buying used isn't your cup of tea though.
I used a set of KRK Rokit 8 G2s for about 2 years and I had learned their sound pretty well and was starting to put out decent mixes after a while with them. I recently upgraded to ADAM A7s and the difference in clarity and mix translation was like night and day, but the ADAMs are also in a significantly different price range than the Rokits, so it's understandable. The KRK monitors have a great build quality to them, but I found the sound quality lacking (especially in the midrange/highend compared to the ADAMs.
This is just what I think though. The best thing for you to do would be to go to a music shop that has pro audio gear and test lots of different monitors directly against each-other. Use test material that you know inside and out to compare the sound of the monitors. Try to listen to how the big picture, and individual things in the mix sound through different speakers. For example when I A/Bed the ADAMs against my KRKs before I bought them, When listening to a quiet section of a mix with an exposed lead vocal I thought the ADAMs sounded like a singer, wheras the KRKs sounded like a good recording of a singer. The stereo image was wider, and the accuracy in the midrange was a whole different animal than the KRKs. Listen for yourself, and then decide what you like!

Another thing that is important for me is that the monitors are pleasurable to listen to. You don't want them to be pleasurable in the sense that they make a bad recording sound good, but in a way that your ears just enjoy hearing for long periods of time. The ADAMs did this for me, perhaps something else will do that for you!
