Brands of the World - Open source database of brands vector logos
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!
LogoSear.ch - Instant search through 200K+ SVG logos from 100+ sources
Flaticon - A database of free vector icons.
Fontello - Tool to build custom fonts with icons.
VectorWiki - A huge repository of ~120K brand logos in SVG format for free and quick download.