Not sure what the best DK leveling spec for patch 3.3 is? Well, as always, Unholy is going to be your best bet. The spec has strong healing skills thanks to extra diseases (meaning better returns from Death Strike), high survivability, strong cooldowns, and a pet you can trade aggro with for especially hard pulls. It also has a few mobility improving talents, which can actually be more valuable for leveling speed than any damage or survivability talent. Here are the 'must have' talents for any Unholy leveling spec:
Ravenous Undead
On a Pale Horse
Night of the Dead
Master of Ghouls
Improved Unholy Presence
Everything in the last four tiers of talents *
* You can skip Scourge Strike as you'll find yourself using Death Strike for its heal instead, when leveling
Here are some talents that look good but should be skipped:
Unholy Command
Corpse Explosion
Unholy Blight
Ghoul Frenzy
Do not get more than 55 or so talents from Unholy, then move over to Blood for the rest; the talents there are self-evident, as all the appropriate ones are basic increases to thinks like raw damage, crit rate, and Runic Power generation.
Finally, you'll have access to two Major Glyph slots while leveling; I recommend Death Strike and Ghoul. You can also swap Dark Death or Death Grip for Death Strike, based on playstyle. And be sure that one of your Minor Glyphs is Raise Dead, as it is a major pain to find yourself unable to raise a Ghoul when you need one.
There you have it, the best DK leveling spec for 3.3. I hope you have a fun time leveling to eighty!