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.
SparkFun Electronics provide KiCad library files for many of their products on their GitHub page. These libraries are based on the SparkFun Eagle libraries.