I was actually just looking at an Aggronite set, curiously. I also considered Steelixite but then it summons weather that actually hurts. Here, meanwhile, is my idea for Avalugg.

Avalugg @ Gyaradosite
Ability: Sturdy -> Mold Breaker
Type: Ice/Dark
Stats: 95/147/214/44/76/28
EVs: 248 HP/8 Atk/252 SpD
Careful Nature
-Avalanche/Ice Fang
-Crunch
-Recover
-Earthquake/Rapid Spin/whatever
(GameFreak, please give Avalugg Icicle Crash. Don't make this Flareon all over again.)
I thought of Gyaradosite for three reasons: It improves Avalugg's typing by giving it STAB on one of its limited physical moves (and it's certainly a defensive improvement); it wastes minimal stats and abilities; and, of course, Mold Breaker. This Avalugg is an absolute monster for taking physical hits, and has a nice 147 Atk for dishing out hits in return.
The moves are simple. Avalugg's ridiculously low speed means it's going to take a hit, and Avalanche capitalizes on this for a consistent 120 BP. Ice Fang is also an option, but is generally inferior unless you're trying to catch something on the switch, and even then you have coverage moves. Crunch is a nice secondary STAB with the possibility of lowering Defense. Recover is, well, recovery. In the final slot, you have options. Avalugg has access to Rapid Spin just in case, and being able to threaten the majority of spinblockers is incredibly handy. If you have a hazard remover already, you can run Earthquake and get that famed Ice/Ground coverage (QuakeBeam? CrashQuake? I got nothing).
248 HP EVs apparently hits a Stealth Rock number (or so says the Smogon Dex; its HP stat is unchanged), which combined with 252 SpD EVs and a Careful nature maximizes its special bulk--which it needs, because this is still going to die if any Fire-type so much as looks as it funny. (I'm using the remaining eight to give it just a little punch.) With that said, you have a very nice offensive tank, capable of taking (physical) hits and dishing them out without much of a problem.