In addition to Subaruguru's good suggestion, I would recommend you look at M&K's line of tripole speakers. I have a pair of the SS-150 THX tripole surrounds, and find they blend very seamlessly with my Vandersteen main and center speakers. It is sometimes difficult to get a good match between planar/electrostatic speakers and dynamic speakers, and that is one reason the tripole design might work well.
M&K has several new tripole models that sell for as little as $400, with prices up to around $2k. Check out their web page listing surround speakers at the following link:
http://www.mksound.com/surround_speakers.html