Oh my God, don't make me choose.
I'm not claiming these to be in order necessarily, but I'll just list seven of my favorites (not counting "Under Pressure" because that would just make this whole process that much harder
).
1. Station to Station
OH MY GOD. Ten minutes and twelve seconds of perfection. Once the song kicks into high gear at around 5 minutes in, it's just unstoppable. "IT'S NOT THE SIDE EFFECTS OF THE COCAINE, I'M THINKING THAT IT MUST BE LOVE"
x infinity
2. "Heroes"
One of the best love songs, ever. Seriously. Despite some questionable lyrics on the full version ("Cause we're lovers, and that is a fact/'Cause we're lovers, and that is that"), it's almost impossible to match this song's raw emotion and power. Oh God. It's so good.
3. Space Oddity
The single that started it all. Such a great song, with cool spaceman imagery in the lyrics. Classic.
4. Changes
Turnnnn and faceee the strangeee
5. Sound and Vision
Awesomely great and innovative song that is as cool as it is tuneful.
6. Golden Years
What a fantastic single. It's got everything, even FINGERSNAPS.
7. Modern Love
A definite contender for his best post-70's song. So catchy and great it just kills me sometimes.
Others that are strong contenders:
The Man Who Sold The World
1984
Ashes to Ashes
Fashion
The Heart's Filthy Lesson
Strangers When We Meet
Thru These Architect's Eyes
Scary Monsters
And a whole bunch of other ones
The guy's a GOD.