Theme Suggestions:
Dragon Stuff: All things dragon related. Alternate dragon (or dragon-related) creature models (there are a ton of different ones from different regions that are not well-represented in NWN), dragon-themed clothing/armor, dragon-themed weapons, dragon-themed miscellaneous items, dragon-related placeables, dragon-affecting spells, short prefabbed cutscenes involving dragons, dragon-themed visual effects, dragon sounds (also good for dinosaurs), prefabbed dragon NPCs (with interesting descriptions, conversations, etc.), prefabbed dragon-related items (with nice descriptions and history to go with any properties).
Elven Stuff: Sure, there are a few weapon models already available, and a suit of elven chain armor (a robe) out there, but what of everything else for surface (non-drow) elves? Graceful statues and artwork, organic-looking weapons, houses grown from large trees, elven fortifications, elaborate crystalline structures, elf-style furniture, ethereal music, nature-themed cloaks, artistically carved wooden shields, additional small animals as familiars/companions, holy symbols tied to FR and non-FR elven deities, prefabbed items made by elves (with descriptions, history, etc.), prefabbed elven NPCs (with interesting descriptions, conversations, etc.), and anything else elf-ish. Not just recolors of existing drow stuff...the surface elves need some stuff to call their own.
The Bazaar: Market time! Merchant stalls, placeable wares of all sorts, sounds, prefabbed NPCs to fill the bazaar (both selling and buying), scripts for dealing with thieves, scripts for stealing, scripted bartering systems, entertainment (jugglers, firebreathers, sword swallowers, performing bards, etc.), merchants with inventory that changes over time, NPC pickpockets, prefabbed items for merchants to sell (with nice descriptions, not everything needs to be valuable or magical). Things to help bring a market or bazaar to life and provide more variety.