Here is a list of some of the academic papers which I have come across concerning cell assemblies and Hebbian learning. These should act as a fairly good introduction to the subject.
Braitenberg, V. (1985) "Some Arguments for a Theory of Cell Assemblies in the Cerebral Cortex", Chapter 5 of Neural Connections, Mental Computation, Nadel, Cooper, Culicover & Harnish (eds), MIT Press.
Hebb, D.O. (1949) "Organisation of Behavior", pub. John Wiley & Sons, New York.
Hetherington, P.A. and Shapiro (1993) "Simulating Hebb cell assemblies: the necessity for partitioned dendritic trees and a post-not-pre LTD rule". Network: Computations in Neural Systems Volume 4, pages 135 to 153.
Pulvermüller, F. (1999). Words in the Brain's Language. In Behavioral and Brain Sciences Volume 22, pages 253 to 336.
Rochester, N., Holland, J. H., Haibt, L. H., & Duda. W. (1956) Tests on a cell assembly theory of the action of the brain, using a large digital computer. IRE Transactions on Information Theory, volume 2, pages 80 to 93.