After reading this comprehensive post on branding by Sarah I wanted to expand and include a few additional resources. I figured it was too much for the comment section so here's my list of favourite graphic design resources:

Logo 

All of your branding starts with a logo. GraphicSprings is a great resource to try out different logo concepts.

Fonts

If you are looking to find a cool new font that you can download for free 1001freefonts is a great resource. 

Icons

Using professionally designed icons can easily take your presentation or website to the next level. Give Flat Icon a shot. 

Images

Your social media posts, presentations and flyers need beautiful imagery to convey your message. Pexels is one of my go-to resources for free high-res images. 

Fellow Ulules let me know your favourite resources in the comments!