Here are a few of the links I've found to be of great use and interest related to NWN2.
NWN2 Blog - This is the Neverwinter Nights 2 Blog by Rob at Obsidian. A must read!
Reserved TLK Ranges - This is for reserving custom.tlk ranges to avoid conflicts with other community content.
Reserved 2da Ranges - This is for reserving lines in the 2da files used by NWN2 (spells, feats, etc) to avoid conflicts with other community content.
NWN1 Custom Content Guide - While this is for NWN1, many of the fields in the 2das are the same for NWN2. This is a great starting place for learning what the columns and their values are for the 2da's.
Player Resource Consortium's PrC making guide - This is a great starting tutorial for creating new PrCs and feats.
Prestige Class Requirements - This link includes the values allowed for the CLS_PRES_* 2DA file. It seems to be missing the RaceOR stuff that the Arcane Archer uses but I need to double check that.
Custom Icon Tutorial - This link shows how to create custom icons for use in NWN2.