Everything here is subject to change and additions. If you can see a mistake or notice something is missing please say so and it shall be changed. The goal here is to use community collective knowledge to get as close to the truth as possible.
An item is considered Pre-Nerf if it cannot drop anymore. In other words, the possibility of the game generating these stats or items has been physically removed by the coders at Anet, mainly 2005/2006 around the release of Factions. The only way to acquire Pre-Nerf items is through trading with other players.
minus 50hp Major runes, all versions
Superior runes with Minor rune icon
Superior runes with Blue colour
Superior or Major runes which remain unsalvaged on a Blue and Purple armor/garb item
Major runes with wrong icon / blue colour (such as absorption, major vigor and recovery, clarity, purity and restoration)
Any Mixed dyes
Vial of Dye with 25 gold value [currently 1g]
Bolt of silk with 30 gold value [currently 15g] (Could be similar for other materials)
Jade Wind Orbs
Brick of Mud
Olias's resignation letter
Tattered Girls cape
White Staff Wrapping
Festival hats that are Rune/insignia-able
If anybody has screenshots of any of these items please post.