The Operation Nightmare page details the new level 55 nightmare-mode operations (Terror From Beyond in 2.2 and Legions of Scum and Villainy in 2.2.2). There's also information on the high-level underworld crafting plans, guild and reputation bonuses, and bonus weekends coming to a game near you. The next such bonus XP weekend is June 21st through the 24th, by the way.
The guild rewards program page has the full scoop on why it's so cherry to be part of a SWTOR guild these days. Aside from the free hugs and moral support, there's a substantial increase to gained XP that guilds can provide -- especially if these guilds go on a recruiting spree.