At this time I am aware of the following upcoming GA’s.  I know the first two will be webcast.
[Note: Some links were updated to generic links for the GA when sites were restructured and links were broken.]

Church of Scotland – May 20 to May 26, 2006, Edinburgh
For more info: http://www.churchofscotland.org.uk/about_us/general_assembly
(Link has aged out)

Presbyterian Church (USA) 217th GA – June 15 to June 22, 2006, Birmingham, Alabama
For more info:  http://www.pcusa.org/ga217/

Presbyterian Church in Canada 132nd GA – Begins June 4, 2006, St. Catharines, Ontario
For more info:  http://www.presbyterian.ca/

Associate Reformed Presbyterian Church 202nd Meeting of the General Synod – June 6 to June 8, 2006, location ?
For more info:  http://www.arpsynod.org/synod2006.html
(Link has aged out)

Presbyterian Church in Ireland – June 5 to ?, 2006, Location ?
For more info:  http://www.presbyterianireland.org/About-Us/Structure-Leadership/General-Assembly

Cumberland Presbyterian Church  – Birmingham, Alabama
For more info:  http://www.cumberland.org/gao/

Presbyterian Church in America 34th GA – June 20 to June 23, 2006, Atlanta, Georgia
For more info:  http://www.pcaac.org/2006%20General%20Assembly/06index.htm

Evangelical Presbyterian Church 26th GA – June 21 to June 24, 2006, Rome Georgia
For more info:  http://www.epc.org/general-assembly/upcoming-assembly.html

Orthodox Presbyterian Church 73rd GA – June 21 to June 28, 2006, Palos Heights, Illinois
For more info:  http://www.opc.org/ga.html

Reformed Presbyterian Church of North America 2006 Synod – June 26 to June 30, 2006, Geneva College, Beaver Falls, PA
I have found no specific info on the Synod
Denomination web site:  http://www.reformedpresbyterian.org

Bible Presbyterian Church 70th General Synod – August 3 to August 8, 2006, Grand Island, New York
For more info:  http://www.bpc.org/synod/index.html

Presbyterian Church of Australia, Next General Assembly Meeting on Monday September 10th, Scots Church, Sydney
For more info:  http://www.presbyterian.org.au/