I haven't seen other responses on this, so I'll jump in.
To start with you might want to search on the forums. I asked this same question a year or two ago. Two vendors that come to mind are Adcom and B&K, but I believe others were suggested as well.
The only product I have heard in this category is the Adcom, and I own an Adcom GTP-506. I am underwhelmed by this thing as a tuner.
The "mono" switch doesn't do FM mono - it mixes the incoming signal (whatever it is, CD, FM, etc.) down to mono. This is handy for mono playback (I do use this), but not handy for improving FM sound -- unlike other tuners, switching to mono doesn't reduce background noise.
The tuner doesn't do as good a job of eliminating static as my old Technics tuner (I believe it's multipath distortion that it doesnt eliminate well).
I haven't really listened to this thing as a preamp in my main system, so beyond the tuner it's hard for me to judge. My preliminary impression is that it's a bit bright.
On the plus side, the thing has 2 tuners built in, and three zones, so you can use it to control your whold house!