MyResourceLibrary
Some brands will share 3D models here. You can sign up for a free account and browse through their catalogue of vendors. Most have Revit and AutoCad files as well as spec sheets.
Technology (CAD, REVIT, Sketchup)
Syncronia
Italian-based upscale furniture search with many free 3D downloads for furniture, accessories, lighting, doors, plumbing fixtures, and more.
Revit Families#3D Autocad DWG#3DS Max#FBX Maya#SKP Sketchup#RFA Revit#IFC Data Files#OBJ Blender Maya#3DM Rhino#search library
Materials + Textures3D models and materials for Corona, VRay, Cinema4D, FStormRender - CGMood
3D TEXTURES | Free seamless PBR textures with Diffuse, Normal, Displacement, Occlusion and Roughness Maps.
Texturebox - Free and Premium Seamless PBR Textures, Materials, 3D Assets and PBR Materials
CAD ModelsNBS National BIM Library
More focused on building materials, but you can find doors, windows, hardware, etc.
Configura
Some brands will share their 3D models here (and use this as their configurator), but you need to contact them to get added to their "briefcases." Generally, you can access these on their websites. The files to download aren't always Revit.
ARCAT
Lots of building products. You'll find 3-part specifications, CAD, Revit, etc, but it's best for construction stuff - profiles, soffits, solar panels, industrial doors, etc. - organized nicely by CSI Divisions/Masterformat
Other softwareBIM&CO
Excellent place for downloading Revit files, especially regarding appliances, HVAC, and other equipment. Smeg, panasonic, hitachi, samsung, bosch, etc. - organized by CSI Divisions/Masterformat
Revit Families#masterformat#CSI Masterformat#RFA Revit#SKP Sketchup#GSM Archicad#IFC Data Files#search library
3D Models General
bimstore
Has some more obscure brand revit families (Gresham?) and user-generated content. Some fun objects (including holiday decor and toys)
BIMsmith Market
Excellent resource library for BIM files as well as 3-part specifications. They have a nice selection of doors on the platform.
Revit Families#specifications#cutsheets#3DS Max#IES Photometry#RFA Revit#SKP Sketchup#GSM Archicad#IFC Data Files#2D CAD#search library