Abstract State Machines
formal method for specifying and verifying algorithms. Tools, meetings, researchers in the area.
http://www.eecs.umich.edu/gasm/
ACM SIGACT
Special Interest Group on Algorithms and Computation Theory, the ACM special interest group for Theoretical Computer Science. Site has membership information, meetings, reports and a newsletter for members.
http://sigact.acm.org/
Dictionary of Algorithms, Data Structures, and Problems
dictionary of algorithms, algorithmic techniques, data structures, and archetypical problems, with related definitions. Many entries have links to implementations, tutorials, and bibliographical references.
http://www.nist.gov/dads/