Milano - San Remo.
It's called "La Classicissima" for a reason. Your overall palmarès may be grand (Cipollini), or it may be non-existing (Gabriele Colombo); but winning this puts you in the history books.
The first really big classic of the season, I look forward to it with great anticipation. Various types of riders are capable of winning, and that makes it interesting (even when it ends in a sprint, it's between only 40-50 guys) - and an edition like this year will stand for the ages.
And this is one of the races that riders treat with the utmost respect. I read an article about Diego Caccia's breakaway last year. He said there that when his break was caught (about 30-40 km out), he "quit". Only that didn't mean he climbed into the team car: He (and all his companions) still finished the race, after being in a 250 km break. 17 minutes down, but they finished. Chapeau.