Mage / Rogue:
Mages have long since been the Rogue's favorite partner for double DPS comps. Both classes have amazing crowd control and burst damage capabilities, as well as the escape abilities necessary to survive the fast-paced 2v2 world. Mage/Rogue synergy has been constantly tweaked by Blizzard, ensuring that it's powerful but not too strong. Polymorph and Sap share the same Diminishing Return category, meaning it's often easier to have your Mage use Polymorph on a target instead of you spending Vanish to get a Sap. Kidney Shot and Deep Freeze are also now on the same DR category, shortening the length of our combined stun lock by a few seconds.
However, I'll be honest: many Mages are currently carrying this comp. A Mage I know (who will remain nameless) is currently floating well above 2000 rating with a Rogue in modest gear and mediocre skills. The Mage in question has 2200 Spell Power unbuffed (2500 when he uses his Mana Gem, don't even talk about when a trinket goes off) and can single-handedly destroy any target in just seconds. The Rogue's job is to simply Sap one target and Cheap Shot -> Kidney Shot another, while the Mage goes wild. If you know a friendly mage who is sporting some great PvE gear, see if you can recruit them for a few games and watch your enemies explode before they can react.
The key to playing Mage / Rogue is communicating your crowd control abilities. Between the two of you, there's over a dozen different ways to stop an opponent. It's very important to coordinate these efforts, as Blinding a Counterspelled healer will waste a few precious seconds of CC that could be used to finish off your kill target. Learn what CC abilities a Mage has, and communicate with your partner ahead of time to ensure you're not stepping on each other's toes.
Resto Shaman / Rogue:
This comp was not very popular before Wrath due to the fact that Druids were essentially the only viable 2v2 healer. There's also the fact that Shamans were terrible in TBC unless played perfectly, and very few were able to accomplish that level of play. With the introduction of Hex (think Dismantle + 10 second silence) and Riptide (Shaman's actually get an instant heal), Shamans are now among the top 2v2 healers. While they can't compete with a Holy Paladin for raw output or survivability, the ability to destroy a healer with Hex while dispelling the kill target's buffs make them a true competitor.
In my experience playing Shaman / Rogue, I focus on destroying an enemy healer while crowd controlling the DPS as much as possible. If we can force the healer to trinket, the healer is immediately Hexed and we destroy him during the 10 seconds of silence (which is easily followed with a Kidney Shot). Your mileage may vary, depending on the healer and DPS in question.
The key to playing Shaman / Rogue is to remember that the Shaman has no "get out of jail free" cards. After Nature's Swiftness has been used, the Shaman is incredibly vulnerable to being trained by the enemy. Use your defensive abilities like Blind, Vanish -> Cheap Shot, and Dismantle to save your Shaman if he/she is losing the healing vs damage war. It's more important to keep your healer alive than it is to finish a wounded target (in most situations).
Holy Paladin / Rogue:
Combining the completely overbalanced (sounds nicer than overpowered, eh?) Holy Paladin with the most evasive DPS class in the game creates a comp that is frustratingly difficult to fight, let alone defeat. A Holy Pally can clear stuns from their Rogue on a regular basis, ensuring that enemy Rogues and Retribution Paladins are completely thwarted in their kill attempts. The ability to tack an extra 4 seconds on our stun lock with a Hammer of Justice is similarly awesome.
One key to playing successfully is knowing when to call for Hand of Freedom or Protection. While we have many ways to avoid damage, it's often "cheaper" to have the Paladin help you out instead of spending too many cooldowns to get away. Bleeds are a perfect example. Calling out for HoP when another Rogue has Garroted or Ruptured you will clear the DoT and give you time to recover. Also, call out to your partner before you unload a burst into your target: a Holy Shock / Judgement / Hammer of Wrath combo can drop a target from 30% to 0% in just a couple Global Cooldowns.
The key to playing Holy Paladin / Rogue is to let the Paladin handle himself in most situations. They're a very powerful and resilient class to kill, nearly impossible for many DPS. If your Paladin is in trouble and needs help, they should be calling to you for assistance. This allows you to focus on the kill target instead of worrying about your healer's HP pool. The Paladin assists his DPS, not the other way around. If you are both playing defensively, your lack of offensive pressure can allow the opposing side to drink or bandage.
Discipline Priest / Rogue:
Part of what made the Restoration Druid so powerful in Season 4 was their ability to play offensively and yet maintain primary healer status. Cyclones, Entangling Roots, and Wrath spam (for the Resto-kins) were what defined the 2v2 druid playstyle. Priests have captured that in Season 5, with Mass Dispel and Penance giving them significant offensive potency. As Paladin and Mage teams have become more and more prevalent, having a Mass Dispel available to prevent the enemy from resetting the fight has become a godsend.
Mana Burn is still incredibly potent after the change in 3.0.8, and is actually MORE potent against higher mana targets than it was previously. A Disc Priest playing offensively can burn through a Paladin or Mage's mana in seconds and completely remove all of their defensive cooldowns; an opportunistic Rogue can then simply discard them at their leisure. This comp has one significant weakeness, specifically versus other Rogue teams. Without the ability to dispel poisons, Priests are often unable to keep you alive through Wound Poison and an enemy Rogue's damage.
The key to playing a successful Priest / Rogue team is to set up the potent Psychic Scream -> Sap combo. The Priest will fear a target, and as the fear effect is winding down the target will leave combat (note that this doesn't work on classes with active pets). Once the target is out of combat, you can Vanish -> Sap, giving you 2-on-1 access to the remaining enemy. Following the Sap with a Blind (into another possible Sap or Fear) essentially removes the target from the remainder of the game. It's important that you force the CC target to use his or her PvP trinket (and possibly their Undead racial) before attempting this CC combination.
While just about any combination of Rogue / PvP-viable-spec will work, the previously mentioned 4 classes have the most synergy with the Rogue playstyle. I recommend talking with your partner extensively before starting your matches, as communication about expectations (if I see you get stunned, I'll assist) and CC combinations BEFORE you begin playing will make these discussions far simpler. Trying to call out a complex CC chain mid-fight can be tough, but learning to communicate effectively with your team will take you over the top.
Also, don't fret if you are getting farmed by Blood Death Knights who simply pop Hysteria and Icebound Fortitude and go immune to nearly every CC in the game, or if an Arcane Mage two-shots you with some instant cast crits. Their time is coming, and every team is vulnerable to losing if they are completely outplayed.