I remember reading the 20th Anniversary Hardback by Peter Haining called 'A Celebration', it was the first really big hardback book devoted to Doctor Who at that time. In that book, at the back, it listed all the missing episodes. At the time there was 120 missing. They have found 23 since then, and according to the Daily Mirror (large pinch of salt alert), they may have found more.
Finding The Tomb of the Cybermen back in '92 was a big deal, especially as Doctor Who was 3 years into its 'resting' period by that time. It was quickly rushed onto VHS (I still have a copy).
Of course in recent years the big find was recovering the remaining lost episodes of the Troughton story 'Enemy of the World' and 4 more episodes of 'The Web of Fear', this time cleaned up and put out quickly on DVD. The BBC has subsequently re-released The Web of Fear with an animated episode to complete it, the previous release had that episode covered by the use of telesnaps (photos taken from the screen during broadcast). The missing episode 3 was actually recovered alongside the other 4, but went missing, most likely sold to a collector.
I think 39 episodes have been recreated through animation (although my preference would be to re-mount them as live action, using similar looking actors), with another 6 apparently due to be animated this year. Maybe with all the Disney money, Doctor Who may one day ave a complete library of episodes again!