Alright, I have one that actually hasn't been mentioned yet.
http://www.smogon.com/download/sprites/bw/199.png
Slowking @ Leftovers
252 HP / 4 Def / 252 SpD
Nature: Calm
Ability: Regenerator
-Scald
-Psychic / Flamethrower
-Dragon Tail
-Slack Off
Ok, so this isn't a typical spread for slowking, who usually invests in defense a by a bit more than one point, but slowking is very capable of performing as a special wall and still retains it's useful resistances for taking on physical threats, while hitting back harder than most defensive Pokemon.
But hey, you think, HP Grass is a 2HKO! And you know what? You're right! But who gives a fuck when you have regenerator and Heatran locked into HP grass???? Just switch to a grass resist and you get a free turn of set up, while Slowbro barely loses any health after Regenerator. All Heatran's other moves can be stalled out with Slack Off, even the fearsome Fire Blast, which just barely misses out on a 2HKO after leftovers. It can then whittle him down with scald, which admittedly won't be doing much, but since you have virtually no risk of getting KO'd, who cares?
You could also use a more conventional balanced defensive spread, but then you'll be 2HKO'd by fire blast. Still, the advantage of regenerator still applies, and you can switch out to something that can take the hit better, so it still functions as one of the safest switch-ins to Specs-tran available. Unless they carry magma storm I suppose :P that's a real clever solution to the regenerator problem.
Funny note: I happened to have rotom-C as my defender while setting up the calculation since it was the defender for my last calculation, and discovered that this Heatran inflicts a ludicrous 376%-444% to it with fire blast with sun up. So, 4 times over on a 2x super-effective attack. Take out the 2x, and it's still inflicting 404hp MINIMUM to the 107 base Sp.Def rotom-A. That gives a sense of scale of the power we're dealing with here.