Four measurements on each of fifty flowers of two species of iris (Versicolor and Virginica) -- A classification dataset. Fisher's original dataset contained a third species (Setosa) which is trivially seperable.
data(iris)Data frame with species, petal.wid, petal.len, sepal.wid, sepal.len.
Andrews, D. F. and Herzberg, A. M. (1985). Data. Springer-Verlag.
Fisher, R. A. (1936). The Use of Multiple Measurements in Taxonomic Problems. Annals of Eugenics 7, Part II. 179-188.