Skyrim: To be a dragonborn dark knight
Yes, I am playing Skyrim right now, so it's kind of fresh in my mind, but I'd argue, at the very least, that Skyrim's relatively flexible spec system allows you to play something similar to a death knight. For example, right now my Dragonborn is using heavy plate armor and dual ebony swords I have enchanted with frost and fire and renamed Lichborne and Hellmouth. While he mostly beats people (and dragons, giants, and bears) up with the swords, he also has a decent amount of work in conjuration tree, summoning and/or resurrecting undead minions. Once I get to level 100 in that skill, I can even get me a perma-ghoul if I want.
Where Skyrim really shines as a death knight simulator though, is in the Werewolf and Vampire content. While Vampiric powers are a little more thematically consistent, the Werewolf melee prowess and back story arguably fits a bit better with WoW's death knight storyline. Either way, your Dragonborn, much like WoW death knights, ends up with an infection you can't control that must be sated by the blood of innocents. Or just random bandits. Either way.
What's also cool about Skyrim is that the high-end crafted armor already kind of fits the death knight theme too. Daedric and Dragonbone armor have the spikes in abundance. Dragonbone armor is made of literal bones , and Daedric armor is actually made with hearts of an ancient race of godlike beings. I mean, come on, how badass is that?
Diablo II: Death knights, meet grandpa
Diablo II may be old, but it's still a pretty solid game, and has the advantage over Diablo III of having the best Diablo class, the necromancer. Right away, necromancer have a good thematic link to death knights. Despite dealing with death and misery, necromancers are ostensibly the good guys, using their powers to fight the Prime Evils. In fact, many necromancer abilities seem to have actively informed WoW death knight design. On the other hand, mechanics-wise, they're solidly long range casters.
They do, however, have a few skills that could allow them to survive in melee. The Meleemancer often uses high Poison Dagger skill along with Bone Armor (A clear inspiration for our Bone Shield) and offensive curses. This is usually considered a high skill build, since it involves using lots of crowd control curses and the like to allow the normally weak necromancer to survive in melee range.
Me, I tend to go zoomancer, which is a build in which you summon lots of undead minions to overwhelm your enemies, which in an of itself is still pretty death knightish. With a full spread of skill points in skeletons, it's like you're commanding your own personal Army of the Dead that has no cooldown and has no summoned time limit. In addition, if you're an old school death knight who misses Corpse Explosion, you can make it a central point of your build on a necromancer. As it is, some zoomancers still use bone armor and curses to get up close and personal anyway, in a variety of build called the commandomancer. As someone who's favorite death knight archetype has long been the undead commander, commandomancer is the perfect build for me, thematically.
Starbound: Death knights go to the stars
Imagine this. You are a member of a hive mind, forced to play a pre-determined role in a brutal medieval society, locked into service as a knight of a mad king, until one day, somehow, you break free. It's unclear why or how you managed it, but you have free will. As a result, you are ostracized and hunted down, and now you must leave your past behind and figure out how to survive in the vast new world, cursed as you are with a cold, unfeeling body ravaged by your artificial construction. So you climb on your spaceship and head for the stars.
I am speaking of course about the glitch from Starbound, a new 2D sandbox game in which you explore the galaxy, land on a planet, mine it for ore, meet the locals, and ransack their houses and science labs for furniture for your giant mansion you built on that one awesome tentacle monster planet. The glitch themselves are a race of androids built to simulate the progression of a society. However, due to a "glitch" in the system, they've stalled at medieval European. Some of the glitch have broken free of the hive mind and are now attempting to join the modern galaxy. The idea of an outcast trying to fit in is kind of the arc of a few great death knight heroes, Thassarian and Koltira. In addition, most of the glitch racial armor is based on medieval European themes, including the absolutely awesome Doom Lord Armor (that's its literal name) in the screen shot above. Gameplay-wise, it may not be quite death knightish, but I get to swing a big mace around while working awesome dark lord armor, and I can build my own mansion out of the bones of the dead and/or that one weird living planet I landed on, so as far as I'm concerned, it's enough for me.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.