@AndreSilva, here is a classic w/ lots of references: [Data clustering: 50 years beyond K-means](http://www.sciencedirect.com/science/article/pii/S0167865509002323). It says k-means "was
independently discovered in different scientific fields by Steinhaus (1955), Lloyd (1957), Ball & Hall (1965) and McQueen (1967)".