Hello all, I've been maintaining a calendar of NLP and CL conferences for the past four years, and have a new listing for 2008 started that people might find useful:
http://www.cs.rochester.edu/~tetreaul/conferences.html
If you wish to have a conference added or report an error, please feel free to email me. I cull together conferences on this list from ACL emails, linguistlist and corporalist, as well as from fellow researchers emailing in.
Cheers, Joel