Recently I decided to return to NWN2. In the past I usually picked spellcasting classes. Now I decided to select a melee class. I'm planning to make a dual-wielding Ranger. So here's my question. Do you have any suggestions regarding a prestige class for this character? Which prestige class would fit here best? Or maybe it's a good idea to go with a pure Ranger as it gains perfection in dual-wielding on level 21?

I would like to see an answer to that as well. I've recently randomly started playing as a Ranger with dual-wielding path and she is a beast. (Mhm, She. I am playing as a all girl party with, Neeshka, Elena and Qara). I considered Arcane Archer for a while but it looks ELF/HALF-ELF only.

Maybe a prestige class with backstabbing potential? With buffs from Qara and Elena, my Ranger can cleanse an entire floor with her wolfie. Since she has high hide abilities (with hide in plain sight on the way) a backstabbing ability might prove useful. But that's just in theory.

Has anyone tried that?

I was thinking about Rogue multiclass, but would prefer something from the prestige list. Maybe an Assassin would be a good choice? The only downside is that he has to have an evil alignment and I'd like to play with a good character. But maybe I'll consider an evil playthrough after all.

Pure dual-wielding ranger is my favorite class in NWN2, it's VERY strong.
I know it's not what you asked, but, I never tried a single prestige class for rangers :)

Assassin requiring an evil alignment was a bummer for me as well. I even considered cheating, turn evil during level ups and restore back after leveling. Rogue is the only other alternative as far as I can see. Other prestige classes doesn't look like they have anything to offer which the ranger doesn't already have.

Pure Ranger looks solid so far. The animal companion can be very powerful, especially with the Natural Bond feat, effectively removing the -3 Lv penalty. And the Dinosaur Companion is a feral beast. I have picked Dino for Elenee, not my Ranger and that monster is a killing machine. Once, I buffed it with stoneskin, Greater Magic Fang, and the usual AC buffs and watched it kill anything on its path. Such a beauty :)

Some of this depends on your character's personality and stuff.
Duelist makes sense if your character is a nimble, dashing sort.
If the character is kind of rough around the edges and a wild child, maybe a couple levels of Frenzied Berserker. You get a d12 for your HPs and you get Supreme Cleave.
There's Shadowdancer if your Ranger is the type to slip in and out of sight and strike when least expected.
There's Weapon Master if your character is particularly attached to his/her weapon
Dwarven Defender if they happen to be a dwarf and hold dear to a certain cause.

Thanks for the advice guys. :) Right now I'm keen on playing a pure Ranger. From what I've read in other places, it's a killing machine on higher levels. I'm only worried if 12 attacks per round won't be too much. :) I don't like when the game is too easy. Shadowdancer might seem also a good idea. I've also considered Weapon Master, but it's more of a Fighter thing in my opinion. Anyway I have to start as a pure Ranger either way, so I'll see how it goes. I need to play this game more frequently. There are so many combinations of classes that I'd like to try...

You can never go wrong with a pure base class. I'd say I do that at least half the time, simply because moving toward a prestige class might steer me away from how I visualize the character or that it cuts off the chain of cool stuff that class can do. In your case, there is no prestige class that allows you to continue piling onto your favored enemy abilities. You improve your two handed abilities automatically without needing to spend feats.
When I thought about Weapon Master, I visualized a Ranger growing up in the wilderness with a trusty weapon of whatever you'd imagine. Daily, almost constant use of said weapon to hunt, track, defend, forage, etc. brings the character to a level of oneness with whatever that weapon of choice may be. Plus the weapon master does utilize some dexterity based elements which lend some synergy with the Ranger class.

WM could be a nice class, but it needs dedication to one weapon type. I'm planning to shift weapons during my playthrough, so I guess that's not a good idea. Probably I'll stick to a pure Ranger. I'm eager to see these 12 attacks per round... :)

It's nice to have that flexibility so you can wield based on situation. Weapon Master takes that away and it also shines brightest when you can land crits, which, as you know, when it's money time in the NWN2 OC, crits don't help you.

Rangers are AWESOME in NWN2.

Definitely go to at least Level 21 for Perfect Two Weapon Fighting, and Bane of Enemies. Bane is a very Nice damage boost and PTWF is huge number of attacks. Also, do this as a Strength based Ranger, so you get big strength damage on those attacks.

For the OC I finished with a Strength base Rogue 1/Ranger 18/Shadow Dancer 1. Rogue at first level to max skill points, and take the Able Learner feat. You can have full Rogue Skills at every level.

I took the same Character into MOTB and ended with (see attached)

Ranger 23 (PTWF and Bane of Enemies)
Shadow Dancer 1 (HiPS)
Rogue 3 (Rogue skill and 2D6 sneak attack)
Neverwinter Nine 3 (Extra 2D6 Sneak attack, without losing BAB and Flavor).