Aside from games where I don't use the alignment system that basically turn out evil, I have played in one evil campaign.

I had an idea for getting not just evil to work together, but evil and good to work together. When I told the idea to my GM, he volunteered to run it.

Story time:

The god of evil decided that the reason he couldn't get his evil people to conquer the world was because they would always backstab each other. So he decided to make an evil dream team, and tie their souls together so that if one died, they all died (in game terms, they would have a shared hit point pool). He set to work performing the necessary magic for this to take place, but one of the good gods found out about it. It was too late to stop what was happening, so instead, she made her own team of good people that would be able to fight the evil. The god of chaos saw this, laughed his ass off, and mixed up the two groups (and added in some random other people).

So here's what we did. We all made characters independently of each other, and we were told nothing except that they could be any alignment. One of the players didn't think this sort of thing would work, and was determined to prove it, so he made a lawful good paladin. The rest were: true neutral ranger, chaotic evil assassin, neutral evil cleric (necromancer), and I decided to be a lawful evil wizard.

We were starting at level three, in D&D 3.5. We all showed up with our characters and the GM announced that we would have a shared pool of hit points. Each person said how many hit points they had and it was written on the board, and then totaled (as a wizard who tanked his Con, I added in only 3 - some people thought it was more funny than others).

Another fun bit about the blood bond was that we could always sense the distance and direction to other people in the bond with us. So when we started out, we weren't together, and we were allowed to "discover" each other. Being the wizard, I got the okay to have been researching the bond (being a sickly and weak child, I should have died many times, but didn't) before we even met up (this also conveniently made my in-game knowledge match my out-of-game knowledge). With my power to avoid death, and my incredibly high Cha, I, of course, started a small cult. Because of my knowledge of the bond, I was seeking out the other members through my cultists. The first player to find me was the cleric, who was more than happy to join my cult, and we worked together to start building a small army of skeletons and zombies to go with my cultists. The assassin thought it would be funny to have been hired to kill me, so he was. When he stabbed me and found that it hurt him as well, he decided to join us instead (didn't take much convincing).

Finally, the ranger and paladin (who already met on the way) found our lair. The GM ran what was basically indirect PvP, with them fighting their way through our skeletons and zombies. When they met up with us, we had a pretty interesting fight, and I managed to convince the ranger to switch sides halfway through. The paladin on the other hand was determined to kill us all. We managed to incapacitate him, and lock him up. When he came to, even though I clearly detected as evil, I convinced him that I wasn't murdering innocents (I wasn't), and I wasn't even oppressing or enslaving anyone. Surely his god would prefer to see me redeemed and not slain? Shouldn't he be able to use this bond for more good than I did for evil? He wasn't completely convinced, but he was willing to wait and see.

The ranger, whose backstory involved seeking revenge for the death of his family, was easy to convert. I fueled his rage and falsified evidence that made it look like an entire organization was behind the deaths of his family (they weren't). I also made sure to hide all evidence of the death of the head of that organization, so that he could continue "searching" and killing for me forever.

The paladin eventually went mad, and he attempted to kill himself several times. Finally, I convinced him that his god had forsaken him (why else had his god not enabled him to stop me?). He became a blackguard, and joined the rest of us.

One of my earlier goals was to pervert the magic of the bond so that we could all become undead. We went on many quests and finally were able to accomplish it. I became a vampire (I was too much of a people person to become a lich), the cleric became a huecuva, the rogue became a wraith, the hunter became a wight, and the blackguard became a death knight.

As we accomplished this, the "other" team found us. We had one of the most epic battles I've ever played in, and we only just barely succeeded.

Eventually I would go on to conquer the known world, and rule for centuries. The GM had planned on having us make new characters, and play in the world we had helped to create (corrupt), but I ended moving out of state and it never happened.