Invuln/SS is more clearly a 'stereotypical' Tanker combination. It's a great combo, don't get me wrong. But I think a lot of love for that combo comes from being the closest thing in-game to Superman or other characters from comic books (please don't let that summon J_B).
However, I have a Shield/War Mace, and love him. I have heard that Shield/SS is also a powerhouse. I don't think you could really go wrong with any of those three, though.
Let me never fall into the vulgar mistake of dreaming that I am persecuted whenever I am contradicted.
~Ralph Waldo Emerson
"I was just the one with the most unsolicited sombrero." - Traegus
My personal favorite is WP/SS.
It's really the only thing that keeps me playing this game.
It's crazy but I actually replay the same character from level 1 to 50 on different servers.
I'm actually restarting my WP/SS again on the Protector server tonight.
You sir are insane.
I respect you for that 
50 Tanks: Invul/ss, Fire/ice/fire, Ice/em, Stone/fire
WP/Stone, dark/dark, shld/mace
50 Other: WS, SS/dark/sc brute, BS/Regen/WM scrpr, fire/fire/force blaster, rad/kin corr, mind/rad ctrl, ill/storm cntrl
Insane? I once had seven different Inv/SS tanks on Virtue alone.
My recommendations: Inv/Dark, Inv/Stone, or for something different, Fire/Dark or Fire/Stone.
And if you want to hit the other end of the spectrum, a Fire/Regen scrapper is my new favourite character. Talk about carnage.
They ALL float down here. When you're down here with us, you'll float too!
@Starflier
Ok I've been around low these many years, so I sorta know what I'm doing.
Tanks Played to 50
Fire/Ice
Stone/Fire (One I've had a lot of fun with.)
Srappers Played to 50
Dark/regen
DB/WP
Spines/Fire
Brutes: Played to mid 30's
SS/Elec
Stone/Invul
So My first thought was a Shield/WM Never played either of them before (not past 12 anyway) But I started looking at the forums and reading all the love for SS/INV, and was thinking maybe Shield/SS???? Or maybe even just rolling a SS/InV Didn't really love either of those brutes, but the massive SS/INV love cant all be madness can it? Maybe those were just bad combos?