if you're just looking for items that are in the database that do not drop, the following query should give you a general idea. please note that it works under the assumption that all related tables (npc_types, spawn2, spawngroup, spawnentry, loottable, loottable_entries, lootdrop, and lootdrop_entries) are without error (meaning no entries with 0 chance/probability or invalid spawn/loot info). it also doesn't take into account items that are only obtainable via quests, tradeskills, or merchants.
Code:
SELECT `id`, `Name` FROM `items` WHERE `id` NOT IN (SELECT DISTINCT `item_id` FROM `lootdrop_entries`);