Here's some ideas:
Native Guide:
desc -- An exploring unit encounters a friendly nomad.
1) Grants a unit in the field the haste buff for one turn.
2) Pay gold (10) to gain a free scout
Mysterious Ruins:
desc -- Remains of a city from a previous era is discovered nearby.
1) Spawns a ruined city on the map with 1-2 barbarian warriors or 1 skeleton
(would be cool if you could put a small lootable gold pile with them)
2) Late game versions could spawn stronger monsters with better treasure
Angry Earth:
reqs -- a mine, shouldn't happen in the first 100 turns of the game
desc -- A hapless miner puts a pick in the head of an earth spirit
1) destroy a mine, spawn an earth elemental (withered promotion)
Best Friend:
reqs -- active hunter
desc -- A wandering hunter befriends an animal.
1) spawn friendly wolf on same tile as a hunter
2) higher turn count could enable different animals
Death and Taxes: (a personal favourite from Europa Universalis II)
reqs -- a courthouse
desc -- An overzealous tax collector has aroused a mob in his city.
1) remove him (+1 happiness in city for 10 turns)
2) why punish talent? promote him (-1 happiness for 15 turns, +1 gold from courthouse, city riots for 1 turn)
Deathbane:
reqs -- a level 3 or greater unit defeats a barbarian skeleton
desc -- A small chance of a veteran undead slayer unit gaining a promotion
1) gain undead slayer promotion
Van Helsing:
reqs -- an active moroi
desc -- A small chance of a unit in the field turning against his masters.
1) unit converts to barbarian
Heresy:
reqs -- active disciple unit, Order religion
desc -- A novice disciple (less than level 4) commits heresy.
1) arrest and subject to inquisition (lose unit)
2) fine, strip of rank (reduce to 0 experience, remove all levels, +10 gold)
3) lecture and pardon the novice (-10 gold)
Unseelie Congress:
desc -- A druid cultist begins a circle nearby.
1) spawn a barbarian druid and 2 bears nearby -- preferably have them all fortify on the spot
Pardon the lack of descriptions. I'm just tossing ideas out quickly.