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
PNGEgg - PNGEgg is a library of transparent sticker png images for designers.
Freevector - Freevector is a best-in-class platform that provides millions of images, icons, wallpapers, brand logos, and vectors.
Flaticon - A database of free vector icons.
VectorStock - Download Free Vector Art, Stock Images, Free Graphic Vectors, Free Vector Clipart, High-res Vector...