The fourth beta weekend for The Secret World will run from 9:00am Pacific on June 22 to 11:59pm Pacific on June 24. In addition to being the final event -- the full release of the MMO is set for July 3 -- this one is worth a special mention because it'll be open to everyone who signed up for the beta.
If you have yet to do so, it's not too late: Funcom is going to let anyone who signs up by June 22 into the beta weekend. The content itself spans what was featured in the three prior events, plus the introduction of player vs. player modes. You're getting the persistent 200-person PvP and smaller-scale battles in Stonehenge and Eldorado. Seems like a perfectly reasonable way to spend the weekend.