Use the search, as there is a ton of info in regards to this exact question, especially in your price range.
If I had to give my recommendation, it would be the KRK Rockit 5 G2's. I just got a set, and I've never heard more accurate monitors in this price range.
I would agree with Guru about listening before you buy, but that comes with one stipulation: They have to be broken in good. Every set of monitors I've listened on "straight out the box" needed a good 10-20 minutes of
VERY LOUD warm-up, just one time before they are good and broken in for regular use. Until you do that, they usually don't deliver their mids/lows how they should, or they'll just sound scooped as fuck.
I broke in the KRK's i just got with the same record I always use. Works like a charm.
AC/DC - Back In Black @ VERY HIGH VOLUME. By the time you hit "You Shook Me All Night Long", everything should be coming through nicely. And really, who the fuck wouldn't have a good time blasting some A.C. FUCKING D.C. ?!?!