Proto.io offers a great collection of icons to help you achieve your design objectives without needing to import icons from elsewhere. You can browse through the collections of icons or use the search bar for convenience. You can always use the find feature (CMD/CTRL+f) to quickly find anything you want.
There are the following 4 categories of icons:
- Generic icons (you can browse by topic)
- Material icons
- Swifticons
- Font Awesome icons