In addition to the official KiCad libraries, there are other, third party sources for KiCad library packages.
While the following links may be useful sources of library packages, they are not maintained or endorsed by the KiCad project.
Digi-Key maintains an atomic parts library for KiCad on their GitHub page. These libraries are licensed under an agreement similar to the official libraries.
Octopart provides individual KiCad symbols and footprints for many components in their extensive library of components.
SparkFun Electronics provide KiCad library files for many of their products on their GitHub page. These libraries are based on the SparkFun Eagle libraries.
SnapEDA provides KiCad symbol and footprint libraries for their customers. The libraries are freely available and can be found on their KiCad library page. The library license can be found on their terms of service page.
PCB Libraries offers their Professional Edition PCB Footprint Expert product to KiCad users for no cost. Instructions for setting up the Professional Edition license key are available in their documentation.