A couple I've messed around with...
Half-dragon (black) Monstrous Creature (poisoned claws) Giant Octopus Reaping Mauler. (it's cheating a bit to use two templates, but 8 poison saves per round is hard to resist!)
Titanic Creature Leechwalker Monk (flurry of really nasty con-drains...)
Legendary Giant Owl Archivist (a distinctly evil sage-type, for when you want the PCs to be nicely creeped out at their mentor, and therefore more inclined to do their own research and legwork. Give him the Leadership feat and an Umbral Ettercap Druid cohort to make his lair nice and secure...)
Ancient dead (the Ravenloft mummy template) Colossal Giant Scorpion Cleric (apply a cleric's buffing ability to something as this dangerous in melee, and watch out! Makes a wonderfully creepy head of a desert demon-cult, too)