Useful:
W3 Schools - Your one stop shop for coding helpEZGif - For converting other file types into gifs or editing gifs
Texture Town - A neocities site dedicated entirely to background textures
Betty's Graphics A neocitie site with thousands of graphics
3D Gif Maker - Website that lets you make rotating 3d gifs out of imges
Dither Me This - Website that dithers images for you
Gifcities - Searchable archive of old gifs from across the web
Google Fonts - Archive of fonts for your usage
The Spriter's Reource- Archive of sprites from various games
Catland - An archive of Louis Wain's works