Pick a bruiser wih plenty of CC and you'll be doing better than 90% of the tanks out there.

Now if you're looking to be a rampart between your team and the enemy's, Shen/Amumu are the only real options.

Out of the actual tanks.

Shen and Rammus are good soakers.

Amumu and Volibear have good damage.

Leona and Sejuani have good CC.

Taric and Galio have good support.

And now there's Thresh... who has good range?

Shen.
Thread over.

Although he can not necessarily defend [well anyways] his teammates, singed is a beast for dis-positioning and wrecking a team's set up. Building straight ap or ap/hp hybrid will make him incredibly tanky without actually focusing on tank items like shen or malphite.

shen
good damage soaker has some sustain too boot and a global save your buddy can theoretically taunt the ENTIRE enemy team barely happens though.

rammus
good soaking redicilous single target taunt good ult for quickly taking down turrets

volibear
good MS and flip aoe slow and can soak a deceptive amount of damage while peeling the enemy down with his ult has an execute move on top of that

garen
hes a bruiser alright but one that can act like a tank and be a beast about it if you manage to provoke the enemy team good and make em attack you while you towerdive and take a good amount of hits while your team does the cleanup you will win same for mundo mundo takes more damage garen can do more damage.

Nassus can "build pure tank" and still do insane damage if he is allowed to farm.

Cho gath is somewhat difficult to play but great disrupt and is usually tanky and does respectable damage

Nautilus has an insane amount of CC under his belt his passive is a hard CC (granted only 0.5 sec last i checked) soaks damage and has easy to land CC skills

Amumu hi ult nuf said he does max % hp with his W has stun and decent damage

alistair used to be the CC king now is ok, no damage can takea lot of damage in a situational setting (his ult)

Sejuani lot of slows and a stunn ult skill shot can make all the difference.

morgana................................wut?
cmon guys ranged snare and an ult that can stun the entire team.... trolololol

taric the almighty taric he is THE MOST FAVORITE support CHAMPION.

every fighter can technically fill the role of a tank if you choose to build em so.

What about Nautilus guys? He is one of the most intimidating ranks in the League. You see a Nautilus running at you, you run the other way man. His natural tankiness makes him one of the most deadly champions that can gank you. He is the CC king of Tanks.

uhhh i think thresh is a good tank

t the adc into your team diana is a fairly good tank too

Leona is my favourite tank, very good early game burst plus with a decent ADC they will hit for an extra 25-140 damage every few seconds.

leona needs to build tanky more so then others but yes she is a very good pick

Rammus. Forever. He's the perfect champion. Kassadin and Ahri keep getting away from you? Rammus. Need to shut down the super fed ad carry? Rammus. Need to ward the whole jungle? Guess who can get it done lickety-split. Rammus.

Oh no! Rammus, we need to kill some towers!
ok.

Oh no! Rammus, you have 50 hp and they're about to towerdive you!
alright.
roll into them, hit taunt, hit w, hit ult and walk away with 48.

You made it but now Caitlyn, Karthus, and ezreal are ulting you at the same time!
yup.
get to the fountain with 3hp.

beautiful.