In 3.5th Edition, there's a few ways to proceed here, but you will likely have to tread into secondary & supplementary books. This may have an added challenge of obtaining these books for yourself & your DM (who has to moderate your group's game). Considering the Death Knight in WoW is has evil connotations, you might be running against typical group norms (with are generally good, or at the very least neutral characters) & could cause some internal conflicts (which a good DM would spin into adventures).
If you have to stick to the Core Books (like the Player's Handbook) ONLY, the options to consider would be...
* Fighter / Wizard multiclass (if you want to primarily focus on melee)
* Sorcerer / Fighter multiclass (if you want to primarily focus on magic)
* Fighter OR Paladin w/ Blackguard Prestige Class
I will note that characters with 11 or more Paladin levels before becoming an "ex-Paladin" (for committing an evil act or violating your deity's code of conduct & have NOT attempted atonement OR chosen to level up in a class OTHER than Paladin) may trade-in their Paladin levels for equal levels of Blackguard. This is generally beneficial to such characters who embrace evil as they already lost the majority of the Paladin benefits.
If you have access to other books, here's some non-basic classes to consider.
* Hexblade (See Complete Warrior, supplemented by Player's Handbook II) -- BEST OPTION
* Duskblade (See Player's Handbook II)
Hexblade would likely be the best option, but be aware that your character CANNOT be a "Good" character based on the nature of their magical abilities & become a permanent "ex-Hexblade" if they do become good (losing their magical benefits & cannot gain any more levels in the class). You're either Neutral at best or Evil at worst on the Moral axis as they're a bit selfish & potentially cruel in nature. HOWEVER, you can choose whatever you like on the Order axis (Lawful, Neutral or Chaotic).
Duskblades are good second option, especially if have strictly good characters (like Paladins) in your group. They don't have the dark tones as the Hexblade, but have the similar mix of magic & melee abilities. Personally, this is the class the non-basic class I prefer because of that mix. I know I won't have as the same variety of spells (as some of the high-level spells will be permanently inaccessible), but I can beat an enemy into submission if magic doesn't work.
While it's ultimately up to you & your DM to make create & tailor character (to help align to the campaign), I hope this sheds some light on your options.