Monitor Audio Bronze B2 or Infinity Primus.

You can get the Infinity Primus 360 for about $350 a pair right now. If you could stretch your budget just a little you can get an Infinity PS-12 for $300 and have a really good sound for $650 total.

http://www.stereophile.com/floorloudspeakers/605infinity/

http://www.hometheaterhifi.com/volume_10_4/infinity-primus-speakers-10-2003.html See the comments on the use of the PS-12 with the 360s.

If you look around you might even find these NIB for less than $600.