What items are worth more when brought/sold to a specific NPC(s), rather than to a regular merchant?

(Inspired by the 'What items should be saved for turn-ins?' question for Fallout: New Vegas.)

In Oblivion, what items should be saved for turn-ins? For example, Roland Jenseric of The Order of the Virtuous Blood will pay 250 gold for Vampire Dust which is only 50 gold at 100% value when sold to a merchant (merchants on average, at lower mercantile levels, will buy at only around 50% of the value of an item). This makes it more worth it to sell Vampire Dust to Roland Jenseric, rather than to a regular merchant.


Solution 1:

(Made community wiki so others can add)

Item NPC Regular value (gold) Reward when sold or brought to NPC
Ayleid statues Umbacano 250 500 gold per statue; 5,000 extra gold when the tenth statue is delivered
Black Bows Count Marius Caro 70 100 gold
Nirnroots Sinderion 0 One bottle of Elixir of Exploration per set of Nirnroot for the first 100 Nirnroots; 250 gold per batch of 10 Nirnroots afterward (Note that at this point, you may get better value for Nirnroots if you're a master alchemist and create potions with it instead.)
Shadowbanish Wine Nerussa 55 1,000 gold for the first 6 bottles, 100 gold for each additional bottle
Vampire Dust Roland Jenseric 50 250 gold

One-time quest items such as Ectoplasm are not included in the above table.