Starry night is cliche' but it is DAMN good.
Can I just toss in a blanket
Sistine Chapel?
It is simply the most amazing thing I have seen... you could sit there for days on end and never get tired of it. It completely surrounds you and envelopes you.
PS: Funny how this "cultured" thread has like 10 replies.
PPS: BTW, School of Athens is a great pick too.