In addition to this list, NAD. I use one with PSB Images, and I think it sounds just great. It was a huge step up from my old Onkyo anyways. I got it refurbished to save a lot, I don't know if you are ok with that. However, as mentioned, make sure its powerful enough to be considered an upgrade. Ive heard Images with weaker/entry-level/50w NAD amps, and it did appear to be less open and much quicker to distort (and this was from a closer distance) than with my (iirc) 140w/ch amp. (and, no, fmw, it was not a double-blind test scoring 100 points out of 100 points, so take it with all the salt you need please, thanks, it was at my dealer's when I did a 4 bookshelf shootout, searching for gifts...).
Another rec could be Outlaw, perhaps their monoblocks x2 for $650 total. I see on Audiogon the older generation of their monoblocks going for $175 used or $225 new. I do not know how they compare to the newer version.
Good Luck!