Isometrica - 3D illustration constructor with 380+ isometric objects
LostGeometry.xyz - Huge set of 91 abstract 3D objects in various styles.
Characterz - Biggest diverse mix and match 3D illustration library
Womp - 3D Made Easy
Khagwal 3D Illustration Library - Free 3D illustration library for web & mobile app designers
Spline - Design tool for 3d web experiences