Top of my list it has to be Strade Bianche. It has drama, early season unpredictability, a spectacular finish set in medieval town of Siena. Pave', dust, gravel, stinging little climbs followed by dangerous descents. The winner is usually the type of rider I admire the most: Gilbert, Cancellara, Moser.
Giro di Lombardia is another race I love watching. Its hilly course and stunning views contribute to the mystique of this end-of-season monument. The Ghisallo climb is iconic in this course often mired by foul weather which adds to the epic efforts of past winners.
Brabantse Pijl is the opener for the Ardenne Classics. I believe its course is actually better than Amstel or Liege, offering a bit of all types of terrain. Even in the wet it's an exciting race to watch. Winding, cobbles, sharp climbs.
Fleche Wallonne is the best of the Ardennes tryptic in my opinion. Amstel and Liege have a great finale but rather unexciting course. The fearsome Huy is incredibly steep and is long enough to cause havoc in the peloton. The favourites here are not always successful.
Milano-Sanremo is the longest race of the year, its course has been improved in the last few years with the inclusion of a couple more climbs. The Poggio's climb always is theatre of drama which the unfolds in its sinuous descent to the sea. It used to be very much the race for sprinters but it now seems to require a stronger type of rider. It alternates between sprinters and rouleurs which makes it more unpredictable than it used to be.
E3 Harelbeke, is the prelude to the two Northern classics Flanders and Roubaix. It is a good form-tester and has a good mixed terrain. The riders who perform well here usually go on to do well in the following more famous races.
Paris-Roubaix is awesome whether it's dry or wet weather. There are always countless attacks and the winner always has to display an extraordinary performance. Pave galore, sharp turns and not a climb in sight but plenty of surprises with punctures, crashes, beer. The genius in this particular race is the finish in the velodrome. It enhances the spectacle and maintains its link with the past.