CogSci 2009 is a definite - I'm going this July.
Others? I'm looking at (just so that I won't forget about it):
- http://www.cambridgeesol.org/LTRC2010/ (this one is a must!)
- http://evolang2010.nl/ (interesting)
- http://lsadc.org/info/meet-annual.cfm (havent really browsed through it yet)