I've been working on a variant of my Nightblade PvP spec that is still a work in progress but I wanted to go ahead and post about it.
I call it the Gunblade - 38 NB / 15 Inf / 13 MM
This spec generally works on the same principles as Nightblade, but makes a few key substitutions. Namely, you're dropping Blackout and Ranger for Marksman. Losing Blackout hurts, but the build is not viable without it.
Key concept: Gunblade works by using ranged attacks from melee range. A side effect is a nearly-permanent increase in movement speed (from MM skills), so you'll never be kited again. Your goal is to open on an opponent, apply Scourge of Darkness quickly and then go for a point-blank Rapid Fire Shot finish. Meanwhile you are ripping out damage with Dusk Strike and talented-Swift Shot.
Advantages: Compared to my Nightblade beast spec, Gunblade has far greater speed and maneuverability, and is able to deal considerably more damage from range. In close, the Gunblade damage is higher when utilizing Ebon Fury due to adding Rapid Fire Shot.
Disadvantages: Compared to my other Nightblade spec, Gunblade has less survivability when being focus fired, due to not having Blackout. Furthermore, unless you have Ebon Fury up, this build deals slightly less damage in melee range, due to losing a few key Assassin talents.
cast Dusk Strike
cast Twilight Force
cast Swift Shot
cast Scourge of Darkness
cast Rapid Fire Shot
cast Hasted Shot
cast Blazing Strike
Notes: The only melee attacks utilized in this build are Dusk Strike and Blazing Strike, so damage is not considerably lower if you have to stay at range, however you want to melee for Hellfire/Fell Blades procs at the very least. Your ranged shots proc Increased Fire Power, which is important for keeping your damage up. This is another reason to never use Primal Strike.
This build can be more effective against Riftblade or Paragon warriors as you can outrange them and kite using the speed bonuses. It also works very well against mages. It's important to remember that you want to try to be in melee range whenever you can, despite having a wide arsenal of ranged attacks.
This build still bears some refinement, and right now I struggle most against 51Sins who get an opener on me (luckily there's not many of those right :x). Pretty much anyone else I can put away with little effort. Enjoy!