Kotaku reports having found a promotional flyer for Guild Wars 2 that puts the release date on June 28. Yes, that's right - next month. NCsoft haven't committed to a date as of yet, but they have probably been keen to wait a bit to make sure people have played the hell out of Diablo III before launching their game.
It's a rumour for now, but we may very well see another huge PC title hit in just over a month's time.