Crush, quite appropriately, was invented in California. Around the time of the first World War, Clayton J. Powel invented a very refreshing orange soda (so yes, the original flavor of Crush WAS orange).
Dr. Pepper acquired it, and it's one of the cash-cow brands of the Dr. Pepper company.
Orange, grape, and cream soda flavors can be found and bought everywhere. Other flavors are not so easy to find, though I've seen Crush Strawberry, Crush Lime, and Crush Pineapple randomly in the northern part of the US. Other varieties include a peach flavor, a chocolate flavor, a lemon flavor, cherry, apple, and even a birch beer flavor for our Canadian friends.
Crush (particularly Orange Crush) appears with other Dr. Pepper brands as jelly beans, frozen drinks, candy, freeze pops, t-shirts, and a variety of other products.
Crush (and other brands of Orange Soda) surged in popularity in the early 90's when a character on the popular Nickelodeon show Kenan and Kel was obsessed with orange soda.