Anatomy

Reference angle - web tool to visualize the human head in different angles.
Muscle Plus - Buff dudes providing references. From their website description: We feature free macho photo materials on the theme of "Macho," which meets the needs of enthusiasts. All the photos you can download here are copyright-free and free to use, so please give them a try.

Animals

search-photos-by-model-tool - a web tool to find animal heads references based on angle, as well as finding skull references. It can also be downloaded locally and improved with personal photos and 3D models.
Animal Photo Reference Repository - Photografic references of animals, free of AI generated photos.
Macaulay Library - A scientific archive for research, education, and conservation.

Clothing

Lacemade - Gorgeous dress designs. Style is flowy, feminine. Caters to a lot of body sizes so it's cool to see a variety of models showcase the dresses.
Yume Kawa Girl - online shop for cute lolita clothing. Very nice for browsing and seeing their stock of frills and dresses.
Jack Hamm drapery lessons, posted by Helioscope on bsky - Guide on how to draw fabric, folds, clothing.

Objects

Another Gallery of Rotating Food GIFs - GIFs rotating foodstuff
Types of Swords from Every Corner of the Globe - an online shop for swords that also has tons of info on the swords themselves.
Sketchfab - lots of 3D models you can download or look at
ACON - 3D models you can buy. They're specifically for webtoon making and most f not all of them are compatible with Clip Studio Paint

Buildings and environments

Arhiva 'Tzigara-Samurcaş' - Photo archive featuring traditional Romanian architecture. A vast and seminal collection of graphical documents that once belonged to A. Lecomte du Nouÿ and a valuable, unpublished collection of “old” ground surveys made by students of the school up until the Second World War, as well as the heritage and private collections of prominent professors, etc.