pCon.catalog

Technology (CAD, REVIT, Sketchup)
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.
Syncronia
Italian-based upscale furniture search with many free 3D downloads for furniture, accessories, lighting, doors, plumbing fixtures, and more.
Architextures, FAVOURITE
Materials | All | Material Library
3D models and materials for Corona, VRay, Cinema4D, FStormRender - CGMood
TextureCan - Free PBR Textures and CC0 3D Models
3Dassets.one - The asset search engine
Texture Ninja
Texturer
Texturelabs
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
patternpanda | Texture Library
Textures - Public Domain Textures
Textures | cgbookcase.com
BIM Components
More for Archicad
NBS 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.
Worldwide map files for any design program | CADMAPPER
Textures | FlyingArchitecture (RALs)
SWTEXTURE - free architectural textures
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
Pattycake - .pat file editing made easy
BIM&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
RENDERPEOPLE
bimstore
Has some more obscure brand revit families (Gresham?) and user-generated content. Some fun objects (including holiday decor and toys)
Modlar
CGTrader
TurboSquid