Rome or Venice are beautiful places for newlyweds and couples of all ages... I was able to go to Italy with my boyfriend in 2006, and it was an amazing experience. In Florence there´s this bridge, the Pontevecchio, were you can put a locket in a gate, representating your love for each other. Dozens of lockets are left there every weekend, and they´re actually running out of space for future ones XD
But of course, if the person beside you is the love of your life, any place can be the most romantic one
Lots of people mention Paris.... I can´t say, I´ve never been to Paris
too bad... But who knows?