Tome of Dalaran Intellect

Before Patch 4.0.1 removed Dalaran Intellect from the game and replaced all instances of this item with Tomes of Dalaran Brilliance, the Tome of Dalaran Intellect was just a luxury item and had no added functional benefit. Using this book would teach you Dalaran Intellect.

Source
The tome was a limited availability item, purchased for (or less with Kirin Tor reputation) from  found in Sisters Sorcerous of Dalaran.