best monitor speaker under $1k, new or used

I think you need to specify their placement. On a bookshelf, ls3/5 (or derivatives thereof) are quite good, but away from the wall (where imaging can be appreciated, and when a reflex port can be tolerated) I'd lean to spica tc-50/60s, epos es-11 (or m-12), or another speaker I've never heard but which is getting a lot of good press, the green mountain audio europa. Many seem to like the new Quads as well.
Also it would help to know what your amp is since the above speakers vary wildly in sensitivity.

SOliloquy 5.0 has to be close to the best, give them HUNDREDS of break in hours though,,, wait,, maybe close to a thousand,,, Truly fantastic sounding speakers.

Von Schwiekert VR-1's are very good in a small room and will work well with low power. Imaging and bass are good even with close placement to the rear wall. I haven't heard the Spica's but VR-1's are much richer and full bodied compared to the Epos