Have you ever played "Join me in the dark side" type of campaigns?

I was in a 4th Edition game about 2 years ago now. My character was a Drow Wizard. In the world we were playing in Drow were considered mutants and black sheep of eladrin families. Drow were capable of tapping into the underneath of magic and this was considered wrong by normal eladrin.

He was essentially an outcast and was almost on par with the more monstrous races in the setting. My wizard, Neerarin, saw the injustice occuring around him, how dwarves enslaved kobolds, orcs were killed on sight, and minotaur were used in fighting pits. He decided to help create a place where the unwanted creatures of the world could find peace and justice.

With the help of his Half-Orc Ranger companion Garn, Neerarin slowly started to use more questionable methods. He gained the trust of the kobolds and became their Prophet of the Dragon, saying he would help lead them to the dragon who would in turn help them build a kingdom of peace and tolerance.

The other wizard in the party saw this darkness growing in Neerarin (using out of game knowledge but whatever) and in the end stopped him from awakening a golden dragon. The egg that held the golden dragon was corrupted and a dracolich awakened into the world. Many thousands died in the ensuing destruction and many, including Neerarin and Garn were raised as his servants.

Neerarin awakening as a lich with Garn his loyal companion even in death set about to destroy the dracolich known as Stevarian. Neerarin took revenge upon the wizard that foiled his plans by cutting off his hand, but he still needed his help and the help of the rest of his former companions to restore the world. Eventually after much continued evilness Neerarin and the party destroyed Stevarian and the world was restored. Neerarin and Garn were cleansed of their unlife and together they set off with their kobold followers to build a kingdom in the uncivilized lands to the far west where all would be equal.

So essentially it became "the end justifies the means" kind of deal and he went through a sort of redemption by realizing he needed to destroy the evil that he had helped create.

I have done many. Never planned out, I don't usually GM games with any force to them that requires that kind of thing. However, over time, many of times the players in particular games have found that the "evil" side found itself to be just as passionate and just as believable as the good side. Most of the times, if I can, I make sure that the overarching baddie in my games thinks he is doing good but simply due to worldview he is not.

I have also run a number of games where the world as a whole would be considered evil and the players good but in reality the world was good and the players evil. That one is a hard one to pull off. I usually have to make sure that the explanations for both sides of the struggle have really been thought out.

There was one game I played way-back-when. 2nd Ed D&D. Party of evil characters (except for the Neutral Barbarian). When one of the players was late, we had half-orc long-pork. He was not amused. Two of us were playing bards with very different kits. My bard was petty evil all of the time. The other bard would play nice, then totally and arbitrarily cause grief to large numbers of people at a moment's notice (like a corporate executive). We had a ship full of barely-trained bandits. We pulled into a pirate port with a huge treasure. The old crew was paid, then fired, and we got a crew of experienced sailors. Meanwhile, that old crew was stuck in a pirate port with minimal job experience, and almost no job prospects. They'd only be hired by the most desperate captain, or fall prey to the pirates in need of some fun.
In another adventure, we were supposed to rescue the prince so he could reclaim his throne from the uncle that had murdered his father and kidnapped him. Instead, we broke into the castle, looted the uncle's rooms, and ransomed the prince back to the uncle (pay up or we set him free. If you want, pay 10% more, and we'll kill him for you.)