Could really do with some more interesting treasures from dungeons, come to think of it. Here's a few ideas (I don't know how implementable some of them are, just thoughts) - with an eye to things that are useful/interesting in the early game but not uberpowerful.
Elven Cloak - makes unit invisible while in forest.
Boots of the Aifon - gives water walking, +20% defence on ocean or marsh
Holy Hand Grenade of Antioch - damages everything around unit, one-use only
Clockwork Steed - gives +1 movement, 3% chance of breaking down every turn
Sword of Winter - +40% on Tundra or Ice, immune: Cold.
Stones of Patria - drop in a city for a one-time production boost.