Dragonfire Adept

Dragonfire adepts were a Third Edition class introduced in Dragon Magic and free as part of that book's excerpts (though they are missing their invocations and can't be played with just this info). They are like warlocks in that they get invocations and a new form of attack, which is a breath weapon. Unlike warlocks, they don't have to blow any invocation slots to change their main form of attack, because they get breath effects which are basically like blast and shape invocations except they can't be traded away as you level. While DFAs share a few invocations with the warlock (Walk Unseen, Voidsense and a few others) and a feat exists to take invocations from the other class but 2 levels higher (rarely worth it), their list is otherwise unique to them and they have some goodies that warlocks just wish they could have.

The main toy they get, which pretty much defines the optimized Dragonfire Adept, is Entangling Exhalation from Races of the Dragon. You can get it at level 1, and it lets you cover your foes in sticky flaming bukkake.

Dungeons & Dragons 3rd Edition Classes
Player's Handbook: Barbarian - Bard - Cleric - Druid - Fighter - Monk
Paladin - Ranger - Rogue - Sorcerer - Wizard
Player's Handbook II: Beguiler - Dragon Shaman - Duskblade - Knight
Complete Adventurer: Exemplar - Ninja - Scout - Spellthief
Complete Arcane: Warlock - Warmage - Wu jen
Complete Divine: Favored Soul - Shugenja - Spirit Shaman
Complete Psionic: Ardent - Divine Mind - Erudite - Lurk
Complete Warrior: Hexblade - Samurai - Swashbuckler
Dragon Compendium: Battle Dancer - Death Master - Jester
Mounteback - Savant - Sha'ir - Urban Druid
Dragon Magazine: Sha'ir - Deathwalker - Fleshcrafter - Soul Reaper
Dragon Magic: Dragonfire Adept
Dungeonscape: Factotum
Eberron Campaign Setting: Artificer
Heroes of Horror: Archivist - Dread Necromancer
Magic of Incarnum: Incarnate - Soulborn - Totemist
Miniatures Handbook: Favored Soul - Healer - Marshal - Warmage
Oriental Adventures: Samurai - Shaman - Shugenja - Sohei - Wu jen
Psionics Handbook: Psion - Psychic Warrior - Soulknife - Wilder
Tome of Battle: Crusader - Swordsage - Warblade
Tome of Magic: Binder - Shadowcaster - Truenamer
NPC Classes: Adept - Aristocrat - Commoner - Expert - Magewright - Warrior
Class-related things: Favored Class - Gestalt character - Multiclassing
Prestige classes - Variant Classes - Epic Levels