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/
Analysis Of Algorithms An initiative of attendees of the 1997 Dagstuhl seminar, these pages provide research papers, a bulletin board, and links to researchers and other resources in the field. The focus is on average case and probabilistic analysis.

http://pauillac.inria.fr/algo/AofA/