As you will have almost certainty heard by now two missing episodes of Doctor Who have been returned to the BBC. The episodes are 084 Galaxy 4 Part 3: Airlock and 146 The Underwater Menace: Part Two. These are the first episodes recovered since 092 The Daleks' Master Plan Part 2: Day of Armageddon in early 2004and bring the number of missing episodes down to 106.
You can read details of the recovery on the BBC and at the Radio Times site. The BBC also has some screen shots here and a brief clip from each episode here. Ed Stradling has uploaded a report on the find, with some interview footage, to YouTube.
Galaxy 4 didn't previously have an existing episode, though a large chunk of part 1 exists, the largest continuous section of any otherwise missing episode. It's now the earliest existing episode from season 3.
Underwater Menace 2 now takes the record of the earliest surviving Troughton episode from his successor, episode 3. It's also means that for the first time we have a consecutive pair of episodes from Troughton's first season. This print is known to originate from the ABC in Australia as cuts made to the opening moments of the episode exactly match material recovered from the Australian censor which I believe is one of the scariest sequences seen in Doctor Who.