Agreed on Irelia's tankiness coming from her item build. I remember the first time I played irelia and couldn't for the life of me figure out why people were calling her tanky when she isn't. Irelia is normally built tanky is because she doesn't lose her damage potential with a defensive build. Her True Damage and TriForce procs are sufficient to deal out....wait for it...TONNES OF DAMAGE! She's not a tank because of her inability to peel off enemies that dive onto your carries. That said, good luck trying to peel off Irelia with her passive and Merc Boots.
Lovely discussion on tanks going on here.
Leona, her kit needs a buff. There are several great threads on the NA forums on how she needs to maintain that threat level after she initiates. I loved the suggestion that successful Sunlight procs also reduce her CD. Makes for better synergy and keeps the threat there. One of the more fun tanks IMO and my fav. Voli is a bit different thank most tanks as he lacks hard CC. He is a bruiser/tank. His threat level comes from the damage output he brings and to achieve this he is rather item dependent. Without damage output, he faces the problem of 'Ignore Volibear'. His passive is great bait though. Pair it with Heal and troll away to tower.
Lee Sin and Udyr are more tanky DPS than tanks. I guess another part of what makes a tank is their initation skills. Leona's Zenith Blade, Amumu's Bandage Toss, Rammus' Powerball, Singe's chase and toss.
@moodswingfella,
Don't worry if you have bad KDA ratio as a tank, it doesn't affect your IP or EXP gain. I think.
As a tank, it's okay to die. In fact, you are expected to die first. Something is wrong if you're in a teamfight with full HP and everyone is ignoring you. Knowing your team position and when to initiate is perhaps one of the most important tank-playing skills you will require. Your initiation timing is everything.
Advice to the newer players :
"Don't chase Singed"