If anyone is thinking this sounds fun, but hasn't an idea what to map yet, here are some ideas for some Tolkien mapping projects that haven't been overdone:

The world at the time of the Lamps.

Beorn's estate.

Battle maps of any major engagement, showing troop positions and movement.

Numenor. Surprisingly, I don't think I've seen a non-JRRT map of this defined, important location.

Interior layout of the Lonely Mountain.

Angband or Utumno. Actually, the ruins of Utumno would make a nice location for Middle-Earth gaming. Canonical, well away from established "history" from fairly early on, underground, and justifying all kinds of strange magic, monsters, and features.

Most of the cities/towns. Minas Tirith might be a bit done. This would include underground Dwarf and Orc settlements.

Woodmen settlements of Mirkwood.

Any localized Beleriand maps (the whole map has been reproduced on occasion, but I can't recall any area being blown up and detailed).

A map of Aragorn's journeys. He did a lot of traveling, including off the bounds of the main map.

Or how about the Green Dragon Inn or Bag End, if you want to go small?