I've been to Vegas, Los Angeles, South Beach, Cancun, and the Virgin Islands, either solo or with a regular p4p companion, for a few days of R&R. Each had their unique attractions. All were a lot of fun.
I've also been to Paris, London, Rome, Honolulu, San Francisco, and Chicago on business, and each of these also have good potential for a few days of fun -- either solo or with a special companion, imho.