Important quests quick list:
The Ancient World - needed to enter the dungeon Labyrinth (Lorekeeper Broolol the Keeper of Traditions - The Heartwood)
Mistaken Identity - needed to enter the dungeon Bedlam (Aernya Mistress of Admissions - Umbra)
Bound to the Land - needed to summon Lady Melisande (Frightened Dryad - Blighted Grove)
Wonders of the Natural World - needed to summon the peerless Monstrous Interred Grizzle (Master Coheen the Librarian - Bedlam)
Main Key - Dread Horn - needed to summon the peerless Dread Horn in Twisted Weald (Anathor - Mushroom Cave)
there are more quests, i'll be adding when i have time
but you can check it here:
http://www.uoguide.com/Quests_by_NPC