Brands of the World - Open source database of brands vector logos
Flaticon - A database of free vector icons.
LogoSear.ch - Instant search through 200K+ SVG logos from 100+ sources
Font Awesome - Font Awesome makes it easy to add vector icons and social logos to your website. And version 5 is redesigned and built from the ground up!
IconArchive - Search through more than 735,000 free icons. Browse icons by category, artist, popularity, date. Organize and share your favorites.
VectorWiki - A huge repository of ~120K brand logos in SVG format for free and quick download.