At the top end of the price scale, I like the Muse and the Velodyne HGS models. At the lower end of the scale, I really like the Velodyne FSR-12. They go for about $700-800 used and I really can't hear a difference between it and the HGS-12. I chose models that have high pass electronics that are actually useful. If you go with a good outboard electronic x-over and a sub that lets you bypass its x-over, or you use the sub in conjunction with running your main speakers full range, then the list expands