The largest surviving population of blue whales is to be found off the west coast of North America and the best place to see them is when they migrate to feed in the Monterey Canyon, off California. Prime blue whale season is August/September but is dependent on the abundance of krill so sightings fluctuate. Monterey Bay Whale Watch (montereybaywhalewatch.com, booking in advance is usually necessary) specialises in longer than usual trips out over the canyon to search for blues and I can highly recommend them. Humpback, minke and killer whales are also regular visitors.
Robert Mann