I was wondering,what's the most powerful two handed sword you can get in NWN?

I got a greatsword +3 by the time I finished the single player.

That's an awfully subjective question, because what you find tends to depend on your character class and such. I found very few good swords, probably because my character didn't use em, but...

I'd also say that what weapon is the best also depends upon what feats your character has and what his class is.

I found a Gem Sword, a great sword that is +3 and deals an extra 1d6 cold damage.

My favorite is a bastard sword of wounding with some vamperic regeneration involved. It looks cool ... black blade with a red aura. Using that, I can still use my shield, which boosts my AC by 8 or so.