COGPRINTS - Cognitive Sciences Eprint Archive: Preprint archive open to all researchers - 500 documents in computer sciences.
CoRR - Computing Research Repository: A preprint repository open to all researchers. Indexed in the Networked Computer Science Technical Reference Library - 900 papers.
INRIA reports: 1800 reports from the French Institute of Computer Science, in english (plus PhD thesis in French).
On-line CS Techreports: List of 400 tech reports archives by institutions and countries (1996).
Technical Report Archives in Computer Science (By Institution): List of 150 tech reports archives by institutions (1995).
UCSTRI - Unified Computer Science TR Index: Indexes 14,000 technical reports from institutions archives - accepts archive submissions.