Here's just a few larger tournaments of interest.
May 30 - June 1, 2008
One of the USFA World Series Qualifiers is happening just down the street from me this spring. We do get some US teams up to play for an opportunity to win a berth in Panama City. However, I wouldn't call it one of our largest tournies as they suggest.
http://www.leaguelineup.com/welcome.asp?url=usfapartners
July 3 - 6 2008
The Montreal Challenge or otherwise knows as the Cooper Challenge in Montreal is another excellent tournament that is if you choose a week long. Girls love participating in it and there is always a Canada vs. USA all Star game. Teams are asked to submit their top player and they form two teams to create All Star Teams.
http://www.montrealchallenge.com/
Canada Cup in Surrey BC July 2008
July 12 - 20, 15th Canada Cup International Women's Fastpitch Tournament
July 14 - 20, 7th Canada Cup International Fastpitch Futures Tournament
July 14 - 20, 4th Canada Cup 16 & Under Fastpitch Showcase Tournament
July 17 - 20, 11th Canada Cup Special Olympics Friendship Division Tournament
http://www.canadacup.com