I visited this places for real, years ago, and believe me, they're absolutely stunning.
But, if you are curious about them, and want to take a look without having to come to Italy,
just visit this sites and enjoy ;)
Sistine Chapel - 3D reproduction
More on the Sistine Chapel: http://en.wikipedia.org/wiki/Sistine_Chapel
The Uffizi Gallery - visit everything !!
More on the Uffizi Gallery: http://en.wikipedia.org/wiki/Uffizi