Both Malphite and Amumu were hit with serious nerfs both to their ults and in general because of how strong that combo was.
They are both still seen, but they dont roll faces like they used too.
The tanks that sees the most use right now is rammus. Mundo was getting popular untill people figured out that EC counters him HARD. There is a lot of talk about Alistar, but as a former Alistar player I can tell you he doesnt cut it. There is just something off. Nunu sees use, he is technically a tank though built for AP. A Road of Ages and banshees veil on him go quite well and can work out.
In any case if your looking for a tank to play, Id have to go with Rammus and Nunu right now. Kayle is seen as well, but I have mixed feelings about her. Her ult is great, and combos rediculously with some champions, but I find the rest of her skills lacking.