Tome of Polymorph: Turtle
Eventide Fountain Coins
Anglers can recover coins from Dalaran's Eventide Fountain. Each coin tells a tale: The wish of the person that threw the coin into the water. Everyone from Dornaa to Arthas himself has made a wish. The coins themselves have little value. But anglers that study the history of Azeroth will find them fascinating. The Dalaran Fishing Guide contains more information.
Catching all the coins (and gaining the achievement, "The Coin Master"), rewards the Titanium Seal of Dalaran:
Dalaran Prisoner's Footlocker
Outside the Violet Hold in Dalaran, you can catch a Rusty Prison Key. This opens the nearby Rusted Prisoner's Footlocker, which contains some rare quality weapons or armor, potions, and other items. For details, read Dalaran Fishing.
A curious reward from the Northrend Daily Fishing Quests. The Unusual Compass simply turns you in a random direction every 10 seconds. Like a drunken dwarf on their way home from the inn, but without all the shouting and dancing. View video (of the compass, not the dwarves). Full guide to Northrend daily fishing quests.
There are a few items of junk caught in Outland that have no practical use, but can be sold to vendors for gold:
Strange Engine Parts
Strange Engine Parts can be rarely caught by Alliance from Steam Pump Flotsam pools in Zangarmarsh. Each part starts a quest (level 55+ required). Simply deliver the Strange Engine Part to K. Lee Smallfry in Telredor for 2g 20s.
((The part is described as, "It reads 'Capissen 38' on the bottom." This is a subtle reference to Firefly/Serenity: "Don't ride in anything with a Capissen 38 engine, they fall right out of the sky." - a quote from Serenity's engineer, Kaylee. Smallfry is a tribute to Kaylee.))
The Impeccably Sharp Tooth can be caught from pools in Pandaria by members of the Brawler's Guild. Brawler's Guild Rank 1 is good enough to catch the Tooth. Deliver the Impeccably Sharp Tooth to your faction's Brawler's Guild (found in Stormwind City's Deeprun Tram for Alliance, or Orgrimmar's Valley of Honor for Horde). Completing the quest allows Challenge Card: Razorgrin to be purchased. The follow-up quest - Razorgrin - rewards gold, Valor Points, and the unique Sharkskin Tunic.
There is one raid dungeon "boss" that requires at least someone in the group to be able to fish: The Lurker Below in Serpentshrine Cavern. Simply fish from the "Strange Pool", and eventually you'll "catch" The Lurker Below.
- Dalaran Fishing - Complete guide to fishing in Dalaran. Including Giant Sewer Rats, Rusty Prison Keys and fountain coins.
- Northrend Daily Fishing Quests - Guide to daily fishing quests that start in Dalaran.
- Also in Valuable Fish: What's Valuable?, Buff Food, Supplies, Valuable Gear, Minipets and Mounts, Catching Mr. Pinchy, Catching the Sea Turtle Mount, and Catching Tiny Carp.