This will never be a definitive collection, but it should make it easier for people to obtain some of the harder to get publications of this pioneer.
Of course, the super-classic the one will the "approachablility" theorem:
Some related papers, the first of which is cited in the '56 classic:
Blackwell, D. (1954) On Optimal Systems, Annals of Mathematical Statistics, 25, 394--397.
Blackwell, D. (1955) The Prediction of Sequences, Rand Corporation Memorandum.
Blackwell, D. (1990, est.) Minimax versus Bayes Prediction (Lecture Text, exact date unknown).