While there has been a list of links for custom content tools for quite some time now, there still isn't one for resources. Surely it's about time that someone started one, isn't it? Before you ask why I don't do it myself, I need to point out that I have very limited access to the inet these days. That said I will post a couple that I constantly use and find useful.
1.
Deviant Art and
2.
Obsidian DawnBut really it needs someone to create a propper list and get it stickied.
TR