There are a lot of resources and links by many different people floating around, and those that have been around NWN for a long time or never left might take knowing where to find it all for granted. Here are some links (to many more links, in some cases) and EE-specific information. Maybe they will be helpful to someone. Apologies for any misinformation or critical omission
Tools & Utilities
Blender - It's free, modern, open source, and currently has the most up-to-date tools for NWN:EE.
gmax - a great many older tutorials for NWN modeling refer to this. Still works
NWMax+ - tools for gmax and (I think) some versions of 3dsMax. This is the most recently updated version, but MDA has been out of touch for a bit now. It does not support some of the newer EE fancymap type features, but was practically mandatory for many years, and is still in use by a lot of people today.
NWN Explorer - EE - virusman's update for NWN Explorer, a tool for extracting or browsing game resources either for content creation or reference. "It doesn't detect the installation path automatically yet but you can specify it manually. As a bonus, it supports new mdl parameters: materialname and renderhint."
NwnMdlComp EE - Compile and decompile NWN models - virusman's alpha update for EE, possibly not a lot of testing done on it.
NWN Toolbox - An assortment of utilities, many still in regular use. (eg TGA Flipper, Veltools)
7-Zip, Peazip, WinRar, etc - You need a file archiver for when you distribute your content, even if you're just posting a single .mod on the vault. You probably have one already, but if you don't, any of these are fine.
Tutorials & Reference
Vault-Wiki Tutorials - The newest place for tutorials to live - a bit sparse right now, but more organized and likely to become the go-to collection in the future. In particular check out the Aribethorial for some EE model-modifications, or Do It In Blender! for super basic Neverblender introductions.
File Formats - Technical information on various NWN file formats, as well as some shader support notes.
Rigging in Blender - Rigging a "skinmeshed" model for NWN, also includes a_fa and a_ba templates with dummy daggers and shields.
Merricksdad's Placeholder Tileset - "I set out to produce a 3 height transition tileset with a few crosser types, and leave the tiles untextured, so that anybody building a tileset could use these as placeholders for their own tiles. "
NWN University - A massive collection of guides/manuals/tutorials on various subjects.
Custom Content Guide 3.0 - As mentioned in the comments, this is somewhat out of date, but still has information not yet documented elsewhere.
NWN:EE 2das - Beamdog may include a zip of their 2das with the game in the future, but for now this is a great resource.
The 1.69 Omnibus - This is a ton of information, downloadable and made easily searchable for reference - including the old-old Bioware forums. (It would be great if the old Bioware forums could be included, one day.) This will grow ever more outdated as EE progresses, but is still pretty handy for all that Old Lore, when you're sure someone did this back in 07 and don't remember who it was. Check out Proleric's comment at the bottom on getting it working in Windows 10.
neverwinternights.info - References for many different topics and tools (including some linked already, and many more that aren't), some in particular categories like sound or animation. 1.69 oriented, still very helpful.
Uploading to Steam Workshop - Guides to getting your stuff on the Workshop. Note that as mentioned in this discussion, if you are not already a Steam customer, you'll need $5 in your steam wallet in order to set the visibility of your content to public.
The Bioware NWN Standard Assets. - If you are wanting to modify a standard asset (e.g. model/texture/portrait etc.) you can grab these instead of having to search for them.
Vault forums - Most people are probably familiar with the vault as a download site, but it is also a community of custom-content makers. Lists like (and more extensive than) this have been made many times by the people there over the years.
vaultchat - A Discord server for the vault. (The IRC bridge is no longer functional.)
(The vault, which I do not speak on behalf of, also hosts NWN's Brothers/Sisters/Cousins in Modding, the NWN2 community!)