Now I've tried Several Specs from all of the tree's and DK's are meant to be able to tank or dps or pvp with any tree. But from my experience Blood leaves a lot to be desired as a tank, and I've never been a fan of Frost.

Blood Dps Spec:
This is im my opinion one of the best single target dps specs from any class in the game. The rotation works as thus:
Icy Touch > Plague Strike > Obliterate > Heart Strike x 2 > Runes cooldown > Obliterate > Heart Strike x 4
That rotation + Deathcoiling whenever you can and topping us diseases when necessary will output pretty massive single target dps. And when the patch changes come in allowing Heart Strike to hit multiple targets AoE dps shouldn't be too shoddy either.

51 - 13 - 7 http://www.wowhead.com/?talent=jfVMqh0IsbRxzAoG0x0hZfM

Unholy Dps Spec
This is a damn good AoE spec. Single target Dps wise its outstripped by the blood spec above, but because of how raid trash works these days you'll probably come a lot higher on the damage meter using this AoE spec, but a little lower on the bosses, and after all, its bosses that matter.

18 - 0 - 53 http://www.wowhead.com/?talent=jfVMqZZfMhIxcox0sMcsut

Unholy Tank Spec
This is the spec I use, and I prefer it to Frost tank spec. For many many reasons...but its just an all round good balance between mitigation and threat generation.

13 - 5 - 53 http://www.wowhead.com/?talent=j0EMoZ0xZfgoh0coxxRRcsut

for the people that are intrested in dk tank site's
http://www.tankspot.com/forums/f14/40694-death-knight-aoe-spec-mt-spec-rotations.
and another one i found
http://www.blizzardguides.com/death_knight_tank_guide.html

frost tank
http://www.wow-europe.com/en/info/basics/talents/deathknight/talents.html?tal=0050000000000000000000000003250530102532002301205131351035000000000000000000000000000

unholy tank
http://talent.mmo-champion.com/?deathknight=0050000000000000000000000003050030100000000000000000000035202330020115250101023133051&glyph=042112060504

well so far i like unholy tank the most i tryed out frost aswell but for some reason i have alot of problems with frost
for one alot of spells and i have treath problems as frost
i havend tryed out blood yet but personal thinking i dont think blood is great for tanking maby as offtank

imo frost is the best tank spec but it's realy hard to play it and get a decent treath build with it
with unholy i roughly think i do twice more maby even 3x time's more treath than with frost and it's realy easy to play it

beside this spec's i wondering how other death knights are tanking in heroics because i find it quite hard as a death knight to tank heroic even boss fights i get alot of dmg wile i have 544 defence it still looks that the healer is haveing a real hard time wile if i see for example if a warrior or pala tank haveing no problems at all with same boss
so i guess it's or me or death knights are sireusly gear depended

What would you recommend as a leveling spec Ell?

I've not had any of those sort of problems Lev since my first couple of heroics. We do seem to be a little harder to heal than warriors starting off but when you get enough Parry/Dodge to keep bone Shield up most of the time on bosses you do fine. Plus having 28k health unbuffed helps. Also from that spec you posted it seems like your Dual Weilding, this is a big issue in tanking because unless your expertise capped your going to be getting a lot more parry's from the boss increasing the damage he does to you significantly. I personally much prefer my current spec to the one you posted. I was on 5k Tps last night on patchwerk using a nice big 2H. 5k Scourge strike crits and 6k rune strike crits make for awesome threat. Yes the spec you posted has 1 more Oh S**t button than mine does in Lichborne but i feel my spec makes up for this in other area's. As for what you said about Frost tanking, i can see how in the future it might be good but I personally think atm Frost tanking is just awful for both threat generation and mitigation. Unbreakable Armor has nothing on Bone Shield.

Right, levelling specs, both blood and unholy work well for levelling, as does frost really, you can't go wrong. Blood is great if you want to solo every group quest in the game which you generally can excluding ring of blood style events. But unholy was a lot more fun for me, i kept trying different specs and always came back to unholy. So I'd suggest trying a coupel of different specs and seeing which you prefer playing as. But if you like i could post a lvl 58 levellign spec for both blood and unholy.

Sorry i forgot to mention Lev. I had real problems tanking starting off but i wasn't using all my cooldowns. Now i basically use Bone Shield and Icebound Fortitude whenever there off cooldown on bosses and on almost every big trash pull.
Glyph of Icebound Fortitude is priceless as is Glyph of Bone Shield.
Hope that helps

I'm lvling as unholy DK now. I think it is awesome and a fun spec to play with. Also the talent: On a Pale horse helps a lot with lvling. Gives u a 20% increase in Mount speed. Could solo al my group quest sofar

Too bad they are prob going to nerf bone shield and IBF

World of Warcraft PTR Patch 3.0.8:
Bone Shield: The mitigation has been reduced from 40% to 20%.
Icebound Fortitude now reduces damage by 20% instead of 50%. The amount of damage reduced increases with bonus Defense (to about 35% for 540 Defense, but can go higher).

Yeah those nerfs are minorly annoying, its not exactly like we're overpowered tanks. Its probably just prot warrior's whining again.
But that is sort of made up for by another 20% armour on frost presence and the new rune

Could either of you post some lvl58 leveling specs for blood and unholy? Want to try out both and see which I get on with.

Yeah np. I'll post one of either. I love making specs

Blood - Good for soloing elites. So much self healing never have any downtime. Here it is:
46 - 0 - 3 http://www.wowhead.com/?talent=jfVMqc0IRf0tzuZZc
Once you get more talent points head further into blood to get the rest of blood gorged and by this time you should have a good feel of what you need next. I've missed out hysteria because its next to useless for soloing. Just keep diseases up and use heart and death strikes along with death coil

Unholy - Good for AoE pulls, still very little downtime, get a pet:
0 - 0 - 49 http://www.wowhead.com/?talent=jZZfM0Ixfkx0sMcsub
Once you get more talent points go further down the unholy tree to get Rage of Rivendare and Unholy Blight. Then possibly top off desecration depending on your preference or start heading down blood. This is imo more fun than blood, 4 diseases to keep up and very nice for AoEing down big groups of melee. Plus a pet is always nice. At this level combined dps is > blood but the self healing isn't nearly as good