It is a great resource for free icons and png image archive. I found everything I was looking for my projects. Really very useful.
Pixabay - Over 270,000 free photos, vectors and art illustrations
StockUnlimited - 1 Million+ affordable royalty-free stock photos, vector graphics, icons, infographics & more
Flaticon - A database of free vector icons.
VectorStock - Download Free Vector Art, Stock Images, Free Graphic Vectors, Free Vector Clipart, High-res Vector...
Freepik - More than a million free vectors, PSD, photos and free icons. Exclusive freebies and all graphic resources that you need for your projects
Vector4free - Vector4free is an online platform that comes with unlimited vector art and graphics to use for multiple purposes.