By the time I read your post, I already had dug it up.
Odd items you may find that aren't easily identified:
Amber Ring: Quest item. Keep it when you find it, but it's useless outside of its "dungeon".
Bezel Ring: Wearer is immune to poison.
Bezel Cup: Fully heals the user. It has as many charges as it has gems left on it.
Duble Ring: Doubles health recovery rate.
Green Skull: The only thing that'll hurt the Larkhon.
Ebony Staff: Casts the Swarm spell. Has 5 charges.
Emerald Sword: A very effective weapon against etheral creatures. There are two of these in the game, make sure you find both of them. You'll need them.
Gauntlets of Force: Quest item. Besides acting as a key, it also allows you to cast the 1st level of the Hand of Fate spell, which pushes enemies back 1 square. This ability is actually quite useful in the "dungeon" where you find this item.
Some weapons and their special abilities you should know about:
Arbalest Eternity - Highest damage rate of any ranged weapon
Arbalest Equalizer - Always misses
Great Maul Thunder - 25% to call thunder (screen will shake) and inflict triple damage.
Long Sword Entropy - Chance to hit the wielder with every 7th blow
Death Stick - 5% chance to inflict triple damage
Axe "Dominance" - 5% chance to kill opponent outright.
Rapier "Coup de Grace" - Instantly kills enemies with less than 25% health.
Westwood stick - 25% to instantly kill opponent, One use only.
If armour has any special ability in LoL, the Cluebook doesn't mention it. Stealth, for example, doesn't seem to play a factor.
The cluebook also mentions Kieran's special ability - he strikes faster than anyone else.
For the heck of it, some items that are mentioned which aren't in the game:
Cloud Ring: Reduces damage from Fire attacks.
Talba Ring: Increases Mana recovery rate.
Zephyr Ring: Wearer strikes faster in combat.