Theil–Sen (median slope) estimator, now a Good Article on Wikipedia: https://en.wikipedia.org/wiki/Theil%E2%80%93Sen_estimator

This is a method for fitting a line to a set of data points by finding the median slope of lines through pairs of points. It is robust, meaning that (unlike ordinary least squares) a constant fraction of the data can be arbitrarily corrupted without affecting the goodness of fit.