I would like to second the Stone/Dark recommendation. My main is Stone/Dark and it's a fine combo for tanking. I run two builds, one for tanking in Granite Armor and one for running Granite-less, and both hold thier own against everything I've thrown at him. Build for speed and recharge to offset the penalties, with enough extra defense to softcap and you'll be in good shape. The extra recharge also helps Soul Drain come back faster to reduce the impact of Granite Armors damage debuff.
I went Soul Mastery for both theme and to grab a nice range attack, a solid AoE, and Darkest Night. While I don't need the extra survivablility Darkest Night provides, in situations where I hit the agro cap, it can help cover extra mobs.
While you won't be anywhere close to the fastest killer around, as a stone/dark you will be very hard to take down and still do respectable damage.