My thoughts are that the best value in used speakers under $3,500 are Thiel CS3.6's. Of course, you should be able to get them for a good bit under that. I have them in my 2-channel/HT system, and I use a Thiel SCS3 for center channel. Currently, my surrounds are an old pair of AR TSW-110's, but I am thinking of either two more SCS3's or PowerPoints. In my opinion, Thiel speakers do well on either 2-channel or HT.
Totem and ProAc would probably make my short list, too.
Totem and ProAc would probably make my short list, too.