SensEval/SemEval is a series of competitions in computational lexical semantics. It started out as a competition in automatic word sense disambiguation, but SemEval-2007 started looking a much wider variety of tasks, such as lexical substitution (paraphrasing) and metonymy resolution. Also check out the task list for the most recent SemEval-2010.

SIGLEX is the special interest group on lexical semantics of the Association for Computational Linguistics.

SIGSEM is the special interest group on semantics of the Association for Computational Linguistics.

See the readings in the Natural Language Learning class in Spring 2010 for papers on automatically learning lexical information from corpus data