Best speaker 3k to 4k used?

I too would recommend the Aerial 10T, which I believe continues to be one of the best buys available and pretty easy to find in the upper end of your price range in excellent condition. Unless you have a very large room you do not need a high powered amp to enjoy these speakers, but the minimum recommendation is generally 100 watts per channel. I used a single BEL 1001 MK3A, which is 50 watts per channel for a year or more and was very satisfied considering I traded up from a Classe CA300. Today I use two of the BELs bridged mono (200 watts)in a 13X22 room and that is all the power they need in a room of that size.

What kind of music are you listening to the most?

Thanks for the suggestions so far. I need a versital speaker because I listen to a variety of music. I like female vocals, accoustic, jazz, light classical,and some rock.

Von Schweikert VR4.5's as stated by 'Acuujim'.
You should be able to get into a pair of these second-hand for about $2500. Then start saving to have them sent off to Von Schweikert for their new upgrade, which is about another $2200.
The upgrade will turn these speakers into something out of this World,...they are already a great speaker though!

Dynaudio Contour 3.3 or Silverline La Folia. Dynaudio probably has better integration, but Silverline will go deeper and probably has better midrange.