Just some of my favorite dives here in the good ole continental US of A:
U853 submarine off Block Island, RI
USS Bass submarine off Block Island, RI
USS Burns destroyer off San Diego, CA
Submerged missile towers off San Diego, CA
Eureka/Elly/Ellen Oil Rigs out of the Port of Los Angeles
Southern Channel Islands kelp forests and sea mounts
Coronados Islands (technically in Mexico, but you leave from San Diego)
Esparanza Quarry diving in a marble-walled palace in central Vermont
Cortez/Tanner/Farnsworth Banks sea mounts on the ocean side of the California channel islands (up to 100 miles off shore)
Farallon Island great white shark diving near San Francisco, CA
Blue Shark cage diving in the gulf of Maine
Old wooden shipwrecks in the St. Lawrence seaway
North Florida Caves and Springs systems
Flower Garden Banks off Texas
Duck Island - Isle of Shoals harbor seal diving off the New Hampshire coast
Scallop diving in mouth of the Piscataqua River near the Portsmouth Naval Shipyard in Kittery, Maine.
There's just too much fantastic diving in this country to adequately name it all in a list.