Registration is now open for Hilton's third quarter promotion. Between July 9 and September 30, 2013, you'll earn triple base HHonors points for Friday, Saturday, and Sunday nights stays, and double base HHonors points on Monday-Thursday night stays.
There's a long list of properties that aren't participating in the promotion, so try to book away from those properties if at all possible. I don't see any of the properties I've recently stayed or where I have upcoming stays booked on that list, but as always be sure to check before you book if you're counting on earning this bonus.
I've updated my Hotel Promotions page with the details of this promotion, and all the other ongoing hotel promotions I'm aware of.