/boggle.
I can understand why you're confused with Talents, when people in this very thread trying to help you out are giving you terrible advice... (Riposte instead of Aggression?)
Rather then just telling you what spec to take, I'll try and explain to you why you want some talents over other.
This is going from the assumption that you want to pve and will put at least 41 point in Combat. I won't talk about 'filler' talents, you do what you want there.
Combat Tier 1
2/2 Imp Sinister Strike -
SS is your main ability, lowering the energy cost will greatly increase your dps as well as your combo generation. This is a must have.
3 Filler points: I highly suggest improved gouge even for a pve build. Being able to gouge an add that goes for a healer can be a life saver, the gouge might as well last longer.
Tier 2
3/3 Imp Slash and Dice -
Possibly our Strongest Finisher, certainly the one ability that will give you the strongest dps upgrade. You want to keep it up at all time if at all possible... having this Talents makes that a lot easier and allow you build combo point to use other finisher (while S&D is still up) with greater ease.
5/5 Precision -
Hits is a very important stats for rogues due to Dual Wielding's inherently high miss rate. This is a must have.
Tier 3
2 filler points.
From a pve point of view, this whole Tier is pretty much useless. You might as well take Imp Sprint, is it's the one ability with the most pve use as well as being an awesome pvp ability.
Tier 4
5/5 Dual wield Specialisation -
Another hugh increase to your white damage and another must have.
Tier 5
Bladeflurry -
A great ability all around, Bladeflurry allows you to increase your single target damage a by a significant amount, but more importantly, it gives you a limited degree of Area Effect damage. There's quite a few boss fight where using Bladeflurry to kill adds is all but necessary. For 1 point, this is a must have.
5/5 Sword Spec -
The best dps spec of all the weapon spec, it will increase your dps significantly. It goes without saying that you want it.
Tier 6
2/2 Weapon Expertise -
Currently, this increase your chance to hit and crit by about 1%. Remember that bit about +hit being important?
3/3 Aggression -
While aggression may seem like a small boost, it's a small boost to the one single ability you're going to use all the time. You probably use several hundred sinister strike over the course of a raid night. That little 6% adds up. It doesn't hurt that it also boost Eviscerate as well.
Tier 7
1/1 Adrenaline Rush -
A very powerful ability if used correclty, AR allows you to do a lot of damage on bosses and mow down trash much faster. Combined with Bladeflurry, it can pad your spot in the dps meter by quite a margin. An insanely powerful ability in it's own right, it's also a prerequisite for Suprise Attack. A no brainer.
2/2 Vitality -
Now vitality is a pretty poor talent. The Sta increase is tiny (and not really needed in pve) and the agi increase is even smaller and will barely increase your atk and crit rate. That being said, it is still a dps boost and where else are you going to put the points?
1 Filler -
At this point, you're 1 point short. You can put it wherever you want really, the talents we've skipped are either worthless or pvp oriented. I like Nerve of Steel, since there's a lot of mob that use AE fear/stun, and resisting one of those to keep dpsing is pretty sweet.
Tier 8
5/5 Combat Potency -
This talent is part of the reason why +Hit is so damn important (beyond the obvious) and why you want a FAST offhand. The more hits your off hand get (directly affect by speed and not missing), the more chance you have to regain energy. The more energy you regain, the more SS you're capable of launching. With a fast weapon, combat potency makes a huge impact on your dps.
Tier 9
1/1 Surprise Attack -
Finisher not being dodgeable is a pvp buff, but +10% to sinister strike is huge for your overall dps.
Assassination Tier 1
Imp Evis -
Eviscerate is not a good pve move. You will use S&D and you will use Rupture before it. That being said, in some situation, Eviscerate is useful. Some mobs are immune to Bleeding effect, and there's little point in using Rupture on trash mob that usually die faster then the DoTs duration. This is where you eviscerate. And it might as well do 30% more damage.
Malice -
+5% crit is so good it's stupid. Take it.
Tier 2
Ruthlessness -
Incredible talent. Getting 1 combo point back from a finisher simplify keeping your rotation up... and while it doesn't happen all the time, the proc rate is high enough to make it more then worth it.
Murder -
Good talent. It gets a lot of flak for being limited to only 4 type of mobs. What people don't seem to get, is that once you're out of karazhan, Humanoids, Beasts and Giants makes up damn near 90% of Raid mobs. Same thing for 5 man instance... yeah, it's limited to 4 type of mobs... which just happen to be the 4 most common mob type in the game.
Relentless Strike -
Getting energy back on finisher makes some of them free or inexpensive, in the long run, the energy saved from this talent adds up to a solid dps increase.
Lethality -
So far, we've spent 6 talents points toward making making SS more powerful. This just keep increasing the power of this move (that you use all the time).
Following those guideline will give you
this build . You have 1 point to put wherever you want. It's the most basic and straightforward pve combat dps build out there, but it's also quite possibly the most effective one.