Data sets
From Robin
Famous datasets
MNIST database of handwritten digits
ImageNet - image database with about 500 images per object
Labelled faces in the wild - more than 13000 face images with labels
Planet.osm - OpenStreetMap of the world at over 800gb uncompressed
Dataset collections
UCI machine learning repository - 378 datasets for various tasks and areas
Deeplearning.net list of data sets