I feel like The Noun Project will prove to be an extremely handy site to reference for future design projects requiring any site of icons. The goal of the site is:

The Noun Project collects, organizes and adds to the highly recognizable symbols that form the world's visual language, so we may share them in a fun and meaningful way.

Basically, it's a huge repository of simple icons created in a very clean and professional manner that are distributed for free; for life. An admirable undertaking and content that is quite well done. Just keep scrolling for more goodness.

via JXN BLK and Simple Honest Work.