I don't actually much care for alignment. I think it's a problematic concept to begin with, poorly explained, even more poorly utilized by many gamers out there, and basically, it works best when it's simplified to merely being a team jersey. So, I tend to do away with alignment in games I run.
Whether that's a contributing factor or not I don't know for sure, but what I tend to get is a lot of ... ahem... colorful characters in my campaigns. Characters that, fairly, would have to be called evil if I were to use alignment.
One notable such character I got was Eladkot, a rather pompous sorcerer who was very interested in advancing his career. Making a pit stop in Blackwater, an anarchic pirate haven under the thumb of the dragon-god Toruk and his undead High Priests, he was turned on to a diviner who could possibly give him some juicy clues. Except, well, she was this possessed little girl who did anthropomancy, and read the future in the entrails of sacrificial victims. The rest of the group balked at that, but Eladkot's brain got to whirring.
The session ended, and Eladkot's player sent me an email that he wanted to sneak out in the night, go to the local slave market, and buy the cheapest, weediest gnome or halfling he could find, and take him to the diviner. I whipped up some quick rules for how the divinition worked, and how many clues she could read in the dying gnome's guts, and handed 'em off.
When Eladkot smugly starting trying to convince the rest of the party, at our next session, that he had some great ideas on where to go next, it didn't take them long to guess what had happened. The look on their faces was priceless.
Anyway, Eladkot later came into possession of a scroll with an incantation (3e rule pretty much like 4e rituals) that allowed him to summon Dagon into the world. The PCs were about 6 or 7th level, and topping out the campaign. Dagon was a CR 30 beast from Dragon Magazine. Needless to say, one of the other PCs surreptitiously stole that scroll from Eladkot before he could end the world in a blaze of Lovecraftian horror.
The next campaign I ran, my "Demons in the Mist" game started off with some characters who were a little shady, but basically decent... it seemed. As the campaign evolved, they became much more petty, much cruel and callous, and much darker, however. Maybe it all started when the womanizer swore service to a demon queen not knowing that she was a demon. Maybe it was when the womanizer was killed by the demon queen in a fit of pique and then reincarnated in the body of Fast Times era Phoebe Cates. Maybe it was when the grouchy old captain was reincarnated in the body of a gorilla. Maybe it was when the ditzy half-orc broad had a backstory element that her village had been raided by hobgoblins, another player decided to play a hobgoblin who had been part of the raid before defecting from the hobgoblin army. Maybe it was when they started suspecting (pretty early on) that their patron wasn't really on the up and up, and was playing fast and loose with them in an attempt to smuggle alchemical weapons into the hands of gnoll and gorilla terrorists. Maybe it was when I decided that the pantheon of gods would be made up mostly of transparently obvious iconic D&D demon lords.
Maybe a lot of the responsibility for evil characters that I get in my campaigns is actually mine!
Well, I've seen a nice rash of them even when I don't run. In our Age of Worms game, the gnome sorcerer Fulcrum killed a room full of commoner non-combatants with a fireball right in Greyhawk city, when a doppelganger was trying to set us up. We managed to convince the city watch that the doppelganger had actually killed all those people. A few of the other players, including a smugly self-righteous cleric of Heironeous insisted that we donate to the families of the deceased, so we went to the gladiator pits to see if we could earn them some money. Fulcrum ended up gambling most of it away, though.
In fact, Fulcrum ended up being so memorable that in a later campaign, another player decided to be a favored soul of Fulcrum... although she didn't actually believe in him. To her, the religion was a way to bilk folks out of donations. Her world was rocked to the core when it turned out Fulcrum was real after all. And she was the moral compass of that party; the one who most vigorously resisted Eladkot's ideas.
Why do I bring this up? Well, my current Freeport game is made up of thieves and cut throats. In fact, they've already cut a few throats and if this were a face to face game instead of a Pbp that got somewhat stalled over the holidays, we'd still be only about halfway through the first session. I actually really enjoy the misadventures of shady PCs. There's really nothing that says D&D has to be a heroic fantasy game, although certainly many people play that way and expect that experience.
The iconic literature on which D&D is based isn't necessarily filled with heroes, though. Although Conan, Fafhrd and the Gray Mouser all had a sense of honor, they were hardly paragons of virtue by anyone's calculation. Elric was the prototypical fantasy anti-hero; and I tend to get a fair number of PCs who model their behavior and misadventures after Cugel the "Clever."
I hear a lot of folks say that they can't do evil. That it inevitably breaks down into games that fall apart with players killing each other. I don't understand this, frankly. I've never seen it happen. Even when I was in junior high we didn't have that happen.
Perhaps the alignment issue is to blame. With a focus on alignment, it becomes more difficult to simply develop a character organically and have him (or her) do what would make sense in light of the established personality characteristics. However, as a guy who got interested in gaming because it allowed another venue to work creatively in a fantasy fiction type environment, that's always how I've approached character issues, and I've been blessed with players who, it seems, think the same way. The misadventures of the scoundrels, blaggards and rogues that I've seen over the past few years have been vastly entertaining for me to watch; much moreso than another heroic goody-two-shoes of the type I used to be more likely to play.