Well, this site (about John Suchet's Mad About Beethoven books) says it best, I think.

1770 17 December - Beethoven baptised in the church of St Remigius, Bonn. The date of his birth is not recorded, but since it was customary for baptisms to take place within 24 hours of birth, it is likely he was born on 16 December.

And, as MouseThief said, if it's good enough for Schroeder, it's good enough for me too.

The epitome of the mad genius. What could the Ninth have been had he NOT lost his hearing?

Two good Beethoven sites I found:

The Beethoven Reference Site
Mad About Beethoven

BB,
NightWing