Parasound Halo P3s can be had for under $600, and they punch way above their weight, and come with a remote, if that's important to you. NAD's current pre-amp, the c 165, should go for less than $1000 used, but I hardly ever see them for sale, and when they do pop up they're gone in a day. Anthem's TLP 1 is also rare, but can be had under $1000 used. A lot of people really like the Adcom GFP 750s, there's one for sale now on this site.
If having a remote is important to you, be sure the used unit you are purchasing comes with the remote. Somtimes it can be difficult to obtain one after-market if the unit you're buying is out of production.
If having a remote is important to you, be sure the used unit you are purchasing comes with the remote. Somtimes it can be difficult to obtain one after-market if the unit you're buying is out of production.