Slides from Ben Kuipers on behavior languages
(ppt);
on the 3T architecture
(ppt);
and on potential fields
(ppt).
Slides on action selection using value functions (ps.gz).
A journal article with more details on the initial subsumption implementation:
Brooks, R. A. "A Robust Layered Control System for a Mobile Robot", IEEE Journal of Robotics and Automation, Vol. 2, No. 1, March 1986, pp. 1423; also MIT AI Memo 864, September 1985.
The detail slides from that article.