In addition to working on a few custom mixer builds (which one of these days I'll get the time to finish), I'm always buying things and trying them out (then half the time selling them).
One of the things that I came across at a great price was an ENG mixer. I bought it from a person who makes their living field-recording classical music. The model I bought is an EAA (Electro Acoustique Applique) Micromix:
It is a mixer that was designed for tasks like sound FX and dialog recording for filming. It can be battery-powered or powered via an external power supply. Apparently these were/are extremely popular in the French film industry.
It has four mono inputs, but on my model Pots 2 and 4 can be ganged so that each one controls a stereo channel. The feature that made me realize it was viable for DJ use is that you can cue each stereo pair of channels individually through the headphones.
Sound-wise and build-wise, it's in a different league from any DJ mixers I've used. Definitely has more in common with something like a Studer or Calrec portable console than a Bozak or Urei. Extremely clean and quiet (especially when battery operated), and the per-channel Haufe input transformers add just a tiny bit of coloration and high-end rolloff. It uses Honeywell conductive pots, and it appears almost to have been milled from a block of solid aluminum. I cannot find this out for sure but it seems to have cost between $3000-$4000 new.
It is very small and since all the I/O is located on the sides, the mixer can be laid flat on a table with the knobs facing straight up. For me it's a nice contrast from the "space shuttle" set up with a massive rack full of equipment. There's less between me and the audience.
Another potentially-interesting ENG mixer is the Cooper Sound CS104, which seems to pay homage to the Micromix in its appearance:
Other ENG mixer brands that are well-regarded include Sound Devices and Filmtech.