I've got to put in a plug for my favorite city, Philadelphia.

Big Sur
Honolulu
Palm Springs

Where you go for a weekend depends largely on where your starting point is but I will pretend that isn't an issue - NYC, Philadelphia, DC, Boston, Chicago, San Fransisco, San Diego, Coronado, Key West, Venice Beach, OK anywhere warm and sunny at this point....

cd, we have stayed along Chincoteague Chanel or closer to the Main Street, as beachfront dog-friendly rentals are rare and/or expensive.