Paul McGann, Doctor #8, just recently made a return** to the series in the mini-sode "Night of the Doctor", a prequel to the November 23rd anniversary episode "The Day of the Doctor". From what I've read so far, the anniversary special is set to include David Tennant (Doctor #10), Matt Smith (Doctor #11), and the recently revealed "War Doctor" (first seen in last season/series' finale "The Name of the Doctor") played by John Hurt. I'm a little disappointed that the remaining Doctors (Tom Baker, Peter Davison, Colin Baker, Sylvester McCoy, Paul McGann, and Christopher Eccleston) aren't confirmed has having any part in the festivities...but the fan in me hopes it's just a tightly wrapped secret.
In the meantime, I was able to get my fix of classic Doctors with Big Finish's "Light At The End", an audio adventure featuring Doctors #4 thru 8!*** It wasn't perfect, I'd have liked to see a little more interaction between the Doctors, but it was fun...and it included my favorite Doctor Who villain, the Master!
What's next? Presumably Matt Smith's Doctor regenerating into Peter Capaldi...will it be in the 50th anniversary special? The Christmas special? Who knows, lol! Between now and then I'll enjoy being a Whovian and work on my holiday spirit by spending some time reading the short story collection "Doctor Who Short Trips: The Ghosts of Christmas"!
*ok...if you want to be technical there was another multi Doc story in 1993...another charity special "Dimensions In Time" that crossed over Doctor Who and EastEnders...but it wasn't in continuity, and isn't considered canon, so...the less said the better
**he's been turning out great work on the Big Finish audios, but hasn't played the Doctor on screen since his first and only appearance in the 1996 TV movie
***in what I believe was a clever use of audio from the original series, William Hartnell, Patrick Troughton, and John Pertwee also