Have an escape plan
For classes that have a harder time against rogues than, say, protection paladins, always have an escape plan when facing off against a rogue. World of Warcraft is a big game of rock-paper-scissors, and it happens that some classes and specs simply have a much tougher time against a particular opponent. Take warlocks, for example. Rogues generally eat warlocks for breakfast, so you'll have your work cut out for you. If you suspect there's a rogue in the area, prepare a Demonic Circle ahead of time and make sure to fight within teleport range. Setting it up on a different elevation, such as in the Warsong Gulch flag room, is good and makes the rogue work harder for the chase.
A little help for warlocks
We'll throw warlocks a bone here, considering most rogues see them as free kills these days. In fact, rogues pick out warlocks specifically in a fracas because they're so easy. Some of these tips will help, but in general, if you're a warlock, expect to visit the Spirit Healer shortly. You can choose from two basic pets to have out against a rogue -- a Succubus or a Voidwalker. A Succubus stays invisible and can seduce the rogue when she gets the jump on you. That should hopefully give you time to create some distance. Judicious use of Seduction should allow you to control the fight at least part of the time.
Voidwalkers are not commonly used in PvP, but are actually one of the best pets to use against a rogue. Having it out should discourage a rogue from attacking you because of Consume Shadows. They can also be sacrificed for a shield buff and provide heftier health for warlocks with Soul Link. Affliction warlocks should always keep Curse of Exhaustion applied to aid in kiting. This will be your most important debuff against a rogue in this fight. Speaking of debuffs, apply a DoT as soon as possible -- stack them if possible -- and force the rogue to blow Cloak of Shadows. Don't panic when she does. Keep your cool and try to survive for five seconds then blow a Death Coil or, if you have it, an instant Howl of Terror. Always save these clutch spells for when the rogue's Cloak of Shadows expires.
Perhaps the most fun a warlock can have when fighting a rogue is if she's specced full demonology. A Felguard can return the favor when the rogue stuns you by keeping the pet on defensive and at least 10 yards away. Metamorphosis should also provide a surprising and interesting turn of events with Immolation and Shadow Cleave. It won't guarantee a win against a rogue, but at least you'll give them a slightly tougher time than normal.
Most of the rogues you'll encounter in PvP will be specced assassination. This build offers them a great deal of control, and most of them will only go as deep as Mutilate -- their bread and butter strike -- and then into the subtlety tree for Preparation. The bad news is that there's no real way to tell what spec a rogue is until she starts hitting you. Mutilate is a tell-tale sign, and these rogues generate a lot of combo points very quickly, allowing them to finish with 5-combo point Kidney Shots much more quickly. Preparation allows them to use their cooldowns in quick succession, which they can either use offensively or defensively.
When do you use a trinket against an assassination rogue? This is a tough call because they can very quickly reapply another crowd control effect without taking away from their stride. Unless you're in danger of dying after their opening Cheap Shot -- wait for Kidney Shot instead. At the very least, the next application should suffer from diminishing returns.
Some builds have Master Poisoner and use Envenom as a finisher, which ignores armor. Just to be safe, attempt to cleanse poisons often. This should have the added effect of possibly removing Crippling Poison, a bonus of Deadly Brew. Assassination rogues will have it applied pretty much constantly because of this, so use any poison removal ability you have at your disposal.
Combat rogues are extremely rare in the Battlegrounds. Combat is widely accepted to be a raiding spec and performs comparatively poorly in PvP situations. However, combat provides significant burst, so they aren't to be ignored. The good news is that most combat rogues you'll meet are likely to be less versed in PvP than other rogues. That said, those who choose to go combat in PvP and excel at it are pretty deadly, too. They have fun tools, with those who PvP using combat by choice going for Killing Spree. Properly glyphed, they can use it pretty often, as well.
It's bad news against clothies, and they'll use Killing Spree along with Blade Flurry to generate an insane amount of hits. If you see it proc through a spell alert AddOn... get out of the way. Better yet, get into a crowd. A combat rogue unleashing full Killing Spree with Blade Flurry on a single cloth target can very well kill in a matter of seconds, and they'll likely be wearing more than a few pieces of PvE gear to optimize burst. Pop shields, use an instant cast fear or horror effect, and generally use your best peel at this point to waste their cooldown. A small note for non-warrior melee -- some combat rogues pick up Unfair Advantage, so if they pop Evasion, it's a good idea to move away for the time being.
Combat rogues rely mostly on burst and a lot of physical damage and strikes. Because they work through volume hits, reflective damage abilities such as Retribution Aura or maybe even Lightning Shield will decimate them. These types of rogues are rare and are less fearsome if only because they're not conditioned to expend their combo points on stuns.
If anything, subtlety rogues are hard to find because, well, they're almost always in Stealth. The good news for casters is that subtlety's strength is against non-warrior melee classes as they can use Ghostly Strike and Setup to unleash 5-combo point strikes or stuns while being harder to hit. Hemorrhage is a subtlety rogue's signature move and it will be their basic strike. The bad news? The debuff is physical. There's no way to get it off other than an immunity.
Subtlety rogues rely on their cooldowns the most and are the most likely to use Vanish offensively because they have Preparation, anyway. They do their most damage coming off Stealth, so try not to let them get their opener. It's a taller order, obviously, because they all have Master of Deception, but it's the best advice against a subtlety rogue. A chosen target will also likely have Premeditation applied, so fights with subtlety rogues promise to be fairly quick.
The basic premise against a subtlety rogue is that if you survive the onslaught of two sets of cooldowns, you're likely to win the fight. While assassination rogues are highly likely to play a control game, using stuns and incapacitates, and combat rogues aiming to deal as much burst as possible, subtlety can go either way but use hit and run tactics more commonly. Their only drawback is a weaker Energy regeneration rate than either of the other two specs, but this doesn't hold them back too much.
You've seen one, you've seen them all
Spec differences aside, rogues are generally the same. They are the bane of all cloth classes with the exception of discipline priests and frost mages. Everyone else, unfortunately, has an uphill battle. If you're a squishy clothie, I'm sorry, but rogues were designed to kill you. Kite them as much as possible. Use every ensnaring ability you have from Earthbind Totems to Cone of Cold to Curse of Exhaustion. Bait their Cloak of Shadows, which is their ace in the hole against casters. Melee classes should have an easier time with them.
Just remember that rogues are a cooldown class. The best rogues know when to use their cooldowns, and those will be hard to beat. Force them to blow their cooldowns and hit them hard when between abilities. Use AddOns to keep track of what abilities are on cooldown and what is going to be available. Some classes will find rogues easy to beat, but for those who find rogues haunting their PvP nightmares, I hope these past few posts have been somewhat helpful to you. Now go out there and slaughter some rogues!