A lot of the good ideas were already claimed (ghouls, vampires and lycantropes notably, and I couldn't help but note how Skerple's Goblin class fit the bill...), so I chose to do the Ogre. (scroll down to see the other entries!).
How Ogrism is caught is unknown. Fighting an ogre might trigger it, but there are several reported cases of Ogrism occurring without any recorded contacts with Ogres. It has been noted that it particularly afflicts those eager to use brute force to solve problems, especially when motivated by greed or gluttony.
For each template of Ogre, your HP and your strength goes up by 2
A: Thick skull, Iron stomach
B: Rage, Eater of Flesh
C: Ogre Smash, Hulking form
D: Tough, Boulders, Thick skull
Thick Skull: Roll 3D6, and compare it to your intelligence. If the number is lower than your current intelligence, it is now your intelligence score.
Iron Stomach: you can eat anything organic as food - bones, bark - but prefer meat. You need to eat 2 rations' worth of food to be satisfied
Rage: As per Barbarian Rage, but if you haven't eaten today, you can only stop raging if someone/thing has died.
Eater of Flesh: If you eat a part of a recently slain humanoid (one arm should suffice), you regain 1d6+1 HP. If you are in battle, kill a foe and haven't eaten yet that day, you must save to resist the urge to start eating right away.
Ogre Smash: If you wield a large club two handed, you inflict 2d6 points of damage. Your rage can only be willingly interrupted on a 1 in 6 chance.
Hulking Form: Your hulking form is now too big for most suits of armor. Your thick fingers can't manipulate bows or crossbows, or any other such fine weapons or tools.
Tough: You reduce incoming damage by 1.
Boulders: You can throw a rock with a range increment of 30 feet for 1d6 + strenght bonus dmg.
The Cure: Sages have speculated that Ogrism can easily be cured by a strict vegetarian diet and a period of a year and a day of kindness and lack of violence. However, no known recoveries have been reported.
Design note: This is a powerful class, but it is a risky one. If all templates are Ogre, the PC is now fully an ogre and should probably be retired. I leave the task of creating an Ogre Mage to a more deft designer than I... (edit: oh well)
Words for Yellow: Vampires, Wendigos and more!
Archon's Court: Nanoweapon Poisoning
Walfalcon: the Skablin (?)
A Blasted, Cratered Land: Hero (aka Destiny)
Anxious Mimic: The Oath
The Benign Brown Beast :the Restless Dreamer
Princesses and Pioneers: Mirror-Struck (you could build a campaign around this)
Parasites and Paradoxes: The Doppelgänger
Bubgear Slug: The Abattoir God (this is *amazing*)
Nuclear Haruspex: The Undying (and the originator of the idea)
Meandering Banter: Wizzard Bidness
The Whimsical Mountain: The Fading
The Oblidisideryptch: awaiting the entry - soon!