St Peter in Chains
yup, pretty sure that's a saint buried in the floor.

Michaelangelo's Moses
Michaelangelo's Pieta. AMAZINGLY beautiful. It is now behind bullet proof glass, since some guy tried to hack at it with a knife in the 70's, so you can't get up close, but even fighting for space and looking at it through glass. Amazing. what else can I say??
Bernini's 6 (7?) story bronze altar. 

St Peter- you can kiss his toe and pray for something. You were not supposed to take pictures of this, but I got one before the guards started yelling!

see the tiny bronze statue thing in the upper right hand corner? there is a hole in there where the sun comes through and shines on the meridian line.