Many champs can be build tanky, but if yoiu look for a tank abilities like :
Taunt, Initiation, Shield, Stun and being able to atract enemies attention and take damage :
Rammus - good all around, ahs shield, can take a good amount of damage, good in jungle.
Amunu - he can stun the whole team and if timed well you will win the team fight, also he does some good damage, also good in jungle.
Shen - his ulty is amazing if you watching the map a lot, yoiu can turn fights and help teammates, also very tanky and can do some damage, also good in jungle.
Alistair - he is a bodyguard you can push away enemies and knock them into air, he is played mostly as support on bottom lane, also can be jungled, but need good cooperation from team mates.
Leona - (my most favourite ) she is played as support, she have single target stun and aoe stun, when her shield is on she can tank anything in this game. She will jump into enemy team and harras people in their face, but she is not easy to play tho..
Nautilus - lot of AOE damage, he can also deal good amount of damage, but he is kinda dull or smt..need good timing. can jungle.
Malphite - best tank vs AD (physical damage dealers) he is just rock solid , can jungle.
Galiio - best tank vs AP (magic damage dealers)
Maokai - great harras, good damage, great jungler.
Nasus - I think he is great champ for learning last hitting, because everytime you last hit something with your Q, you will stack up attack damage, if yoiu do it properly and farm a lot yoiu will be immortal with your ultimate on and you will deal tons of damage.
I hope I didnt forgot someone..
So these champs have the mechanics a tank need in team fights, there are also others like Mundo for example, but he has only a skillshot slow, no aoe or taunt or anything to realy grab a skilled team attention. I hope it helps.