The twin spacecraft of the GRAIL lunar gravity mission are set to launch side-by-side on a Delta II rocket on Thursday, September 8. The launch may happen on the 8th in either of two instantaneous launch windows at 5:37 or 6:16 Pacific (12:37 or 13:16 UTC). Here's all the places where you can find information about the upcoming launch. Weather looks a little questionable with, as of now, a 60% chance of the weather constraints being violated on both Thursday and Friday. Every day that the launch is delayed, the two launch windows move earlier in the day by about four minutes.
Start with the United Launch Alliance and NASA press kits for background information on the launch and mission. On launch day, NASA TV will cover everything as usual; I'll probably be watching the feed through Spaceflight Now's GRAIL mission status center. Another good place to watch will likely be JPL's Ustream channel. Also check Twitter -- there will be 150 people at a #NASATweetup at the launch, who hopefully will not go home disappointed!
Here are timelines for a September 8 launch, one each for the 12:37 and 13:16 launch windows. The two timelines are the same in terms of seconds since launch through the first cutoff of the second stage engine at 430 seconds, and after that they diverge.