I went over at San Ysidro on Christmas Day 1981 with my then girlfriend (had a place on Ocean Beach San Diego) to go to Rosarita Beach for a few Margaritas and a Xmas lunch. Being a Brit I didn't have the fears of the locals but I needed to get out in Tijuana for a roadside pee. She was...
San Diego San Francisco and Houston are pretty high up a list but in no particular order:
Galveston
New Orleans
Key West
Fort Lauderdale
Tampa/St Petersburg