I played a Vhaeraun-worshipping Drow cleric once who tricked the party into believing he was a cleric of Eilistraee (before the merger, mind you). He would act the part of a good Drow seeking redemption, while secretly scouting out new markets for Bregan D'aerthe to run their typical schemes of extortion, racketeering, and money laundering. It was fun being a secret Murder Hobo, especially when sometimes the party was hired to investigate my antics.
The trade routes that got opened up between the surface and underdark were quite lucrative, and if a few Iblith got raped and murdered along the way who cares. My character must have left a dozen little half-breed bastards all over the surface of Faerûn.
My Drow character was pretty fucking chaotic evil.
Edit - To be fair though, there's a reason why the Golden Rule is supreme to all others. My current character is a LG Kobold Warlock who hails from a tribe of Bahamut-worshipping Kobolds who manage a city's sewers in exchange for mining rights, and being left to their warrens. When I joined the party as a local guide the first thing I did was scramble up the back of the barbarian character to ride on his shoulders, much to his chagrin. He was really pissed when he woke one day to find a wooden saddle attatched to the neck of his plate armor, but quickly got over it when I started raining down eldritch blasts on his foes.
Picture Conan the Barbarian with a madly cackling 2.5 foot tall Kobold riding him into battle, firing energy blasts from a jeweled pickaxe.
