Bethesda Softworks has announced that Old World Blues, the third Fallout: New Vegas add-on, which was originally scheduled for a June release, will come out on PC, PlayStation 3, and Xbox 360 on Tuesday, July 19th.
Prior to release, Bethesda will also release a new patch for New Vegas, which will add not only support for Old World Blues, but also performance and stability improvements.
They have also released some new screenshots from the upcoming add-on:
Jason Bergman also stated that there are no plans for separate disc releases of the Fallout: New Vegas DLC. If you want to have them on a disc, you'll have to wait for the GotY edition, which is pretty likely to follow the digital download release of all add-ons.