Asimov would have been 94 today... using his 'officially celebrated birthdate'. Isaac actually wasn't sure exactly when he was born, so he decided upon January 2nd, 1920 (it may actually have been as much as month or two earlier, his parents weren't entirely clear on the matter).
I don't know which three movies I consider the best (so many), but this might be a good day to break out The Last Starfighter just because... that movie was fun!
I Robot would be very appropriate for viewing today. Also Bicentennial Man, and Nightfall (haven't seen that one).
The Day The Earth Stood Still (the original) and Forbidden Planet for you classic types.
District 9, Serenity, Contact...
The Day Of The Doctor, because Doctor Who is now over 50 years old! Nicely done too!!!
The Matrix Trilogy, Alien, Avatar...
And Dark Star for the silliness factor!