THE paper on the EM algorithm
Dempster, AP; Laird, NM; and Rubin, DB,
"Maximum likelihood from incomplete data via the EM algorithm." J.
Roy. Statist. Soc. B 39:1--38, 1977.
The LVQ paper:
Y. Linde, A. Buzo, and R. Gray, "An algorithm
for vector quantizer design," IEEE Trans. Commun., vol. 28, pp.
84--95, Jan. 1980
A really good overview paper on clustering
Jain, A.K, M.N. Murty, P.J. Flynn, "Data Clustering:
a Review". ACM Computing Surveys, Vol.31, n.3, pp.264-323, 1999.
Another paper on mixture decomposition, with
a method for determining the number of components
Mário A. T. Figueiredo, Anil K. Jain,
"Unsupervised Learning of Finite Mixture Models," IEEE Trans. PAMI, Vol.
24, No. 3, March 2002, pp. 381-396.
(yes, we teach THE STATE OF THE ART!) :-)