Isometrica - 3D illustration constructor with 380+ isometric objects
Wannathis - 3d illustrations and freebies
Characterz - Biggest diverse mix and match 3D illustration library
Shapefest - A massive library of 3D shapes for everything!
Khagwal 3D Illustration Library - Free 3D illustration library for web & mobile app designers
ccclaymoji - A fun little tool to make emojis that have a fun 3D-like effect.