Meh, I'll assume this was posted already, but whatevs.
Steelix @ Leftovers / Mental Herb
Nature: Careful
Ability: Sturdy
EVs: 252 HP / 252 SpD / 4 Spe
- Curse
- Dragon Tail
- Rest
- Sleep Talk
I saw this posted a lot for Onix, but Steelix can do it well enough as well. Maximize defences with the spread, and be a ResTalk phazer. It may be slower than Onix, but it has superior typing. Lefties helps recovery, but if you're worried about being Taunted in your sleep, Mental Herb is always an option.
Most of its other options have been discussed: the 4th Gen Curse sets, Sheer Force elemental fangs sets, etc. And like everyone's said, most of its offensive capabilities are overshadowed by Ferrothorn. However, Sturdy is truly its saving grace, as you can take advantage of that to set up Rocks w/ Mental Herb, or you can phaze a threat comfortably, provided they aren't behind a Sub / flinching you / have a multi-hit move / Mold Breaker-esque abilities.