Bronzong is the #1 Salamence counter. It can switch in and pose a threat. Avalanche Gyarados does well too. Hell, anything with Ice Beam than can take a hit :-D.
I'm going to have to disagree, since I've been using Bronzong as it's counter up to this point (and it only works on occasion).
Here's my reasoning: Bronzong is usually a lead Pokemon, which means the opponnent knows you have that as a potential counter. If the opponent is a smart player he'll toss out a Fire Blast. A Life Orb Fire Blast from the usual 24 EV in Special Attack does about
55.33% - 65.09% to a 252HP/92SpDef Sassy Bronzong, a 2HKO.
Now let's assume you throw out a bulky water type when expecting the fire blast. We'll use BulkyGyara (since you brought him up). The usual bulkyGyara with 156HP/100Def and Intimidate in effect will take
51.62% - 60.81% from a 252Att Adamant Life Orb Outrage. This Gyarados has already been hit by Fire Blast (we'll say it does about 10%, too lazy to check) and if you're really unlucky, another 25% from Stealth Rock. Thats about 86-95% damage taken trying to counter it, which only gives you about 5-15% room for error (hoping that you don't need Gyarados to counter any other Pokemon). Not great odds.
Now for the sake of argument I'll look at two more scenarios. Let's assume you outpredict the Salamence and come in on a Dragon Dance with Bronzong (252HP/80Def). If he decides to use Outrage on you, you'll take
52.66% - 61.83%. A 2HKO. While in return with Gyro Ball from the usual 86Att Ev's, Salamence will take
87.92% - 103.63%. This is a possible OHKO (it is if you have Stealth Rock up). If you're not lucky and you dont score at least 97% hit, you lose yet again. Not exactly an ideal counter IMO.
One last example, I'll use Suicine (I would consider arguably the Bulkiest of the Bulky Waters). We'll assume Suicine (252HP/252Def and Bold) comes in on a Dragon Dance. It will take
70.30% - 82.92% from Outrage. Gives you only about 18-30% room for error, not too bad, but not great. Now if suicine comes in on an Outrage it will take
47.28% - 55.45%. A highly possible 2HKO (definite 2HKO with Stealth Rock).
In my examples the only thing I see beating Salamence is
amazing prediction. Just
one wrong prediction and the only thing left is to revenge kill (sounds like a certain situation with another Dragon).
Maybe I'm way off base and I actually hope I am (someone please prove me wrong)...but Salamence seems
almost impossible to take down with at least one Pokemon.