TinEye - Reverse Image Search to help find an image's source, duplicates or altered versions.
VisualData - Instagram for Visual Datasets
IQDB - Multi-service image search
NooBox - NooBox is a Chrome Extension that provides useful functions, such as: Multi-engine Reverse image search, Extract Images, Screenshot & Search
SauceNAO - SauceNAO is a reverse image search engine.
Bing Image Search - Now w/ related searches, Pinterest boards, and where to buy