DEA has become a popular subject since it was first described in 1978. There have been hundreds of papers and technical reports published along with a few books. Technical articles about DEA have been published in a wide variety of places making it hard to find a good starting point. Here are a few suggestions as to starting points in the literature.
The first paper was the original paper describing DEA and results in the abbreviation CCR for the basic constant returns-to-scale model. The Seiford and Thrall paper is a good overview of the literature. The other papers all introduce important new concepts. This list of references is certainly incomplete.
A good source covering the field of productivity analysis is The Measurement of Productive Efficiency edited by Fried, Lovell, and Schmidt, 1993, from Oxford University Press. There is also a recent book from Kluwer Publishers, Data Envelopment Analysis: Theory, Methodology, and Applications by Charnes, Cooper, Lewin, and Seiford.
To stay more current on the topics, some of the most important DEA articles appear in Management Science, The Journal of Productivity Analysis, The Journal of the Operational Research Society, and The European Journal of Operational Research. The latter just published a special issue, "Productivity Analysis: Parametric and Non-Parametric Approaches" edited by Lewin and Lovell which has several important papers.