I play Kayle alot since the patch and I must say I am doing quite well as her in a Tank/Supportive DPS role.

My best items are Nashor's and Soul Shroud.. and I usually work towards Atma's but there is another item in between that is rather flexible.

So the choices are:
Warmog's - putting me at just about 4000+ health at 18 - no other bonuses.
Rylai's - 3300 health plus a substantial boost to Fury, Reckoning, and Blessing - however the slow only applies to Reckoning... which makes it better... but maybe not good enough
Frost Mallet - 3500+ health and a decent dmg boost but a even better slow on every attack

Basically I want something to add survivability and something else. AP scales well across all three skills, but phys. dmg. works too.

Any suggestions?

Nashor's is a must, I always get it. I also run a cooldown runes page, because chain Reckoning and frequent ulti is a huge asset.

I'd say stack ability power. It gives you a good nuke in Reckoning, and boosts your attack with Fury. Blessing is also quite good, the healing is not insignificant.

Typically, I'll go
Nashor
Boots of Swiftness
Guinsoo's Rageblade
Mejai

This isn't a tank build though, obviously.

Edit: For tanking, I'd go Armor/Spell Defense over health, because that makes your Blessing that much better on yourself.