If you want to attend a launch event for Diablo 3, complete with long lines, then you better hope you live near Blizzard's hometown of Irvine, CA. It's the only U.S. event planned for the release of the game on May 15.
Blizzard and the GameStop at the Irvine Spectrum have teamed up for the midnight release, which will be attended by many of the Diablo 3 development team and Blizzard executives. Festivities will begin at 8 p.m. PST on May 14. The evnt will include giveaways, contests and some extra video footage that hasn't been seen before.
If you live outside the United States, then you can attend official events in the United Kingdom, France, Germany, Sweden, Poland, South Korea, Thailand, Singapore, and the region of Taiwan.
If you don't live anywhere near Irvine, then contact your local retailers to see when they will have the game on sale. Many retailers are planning to be open at midnight when the game goes on sale.