how old are you and who all is going? what kind of stuff do you like? adventure? relax? both? sun? winter?
I will relate some of my good experiences:
I love the sun and sand, so I would say Mexico. Cancun if you are young and Playa del Carmen if you are old (like me)
Hawaii is AMAZING, Oahu...but it takes $$$ to pull this one off, ack.
Here was a VERY cool experience for me. I got a free plane ticket and hotel room for about 3 days in San Francisco...in the Springtime (my fave time). I had never visited Cali before. I am a BIG loner and I also like to explore. I had VERY little money. So I spent 3 days literally walking from bay to ocean, through the central park, the boardwalk, the golden gate bridge, Chinatown, etc. It was a VERY NEAT city!!! Trollies, Lombard Street, Haight/Ashbury, downtown, etc.
I got around the whole town on my feet, or on busses (they had these old busses that were converted to electric) or trollies.
The only part of it that I didnt like was a couple of times I actually wished that I had someone to share it with.
So pick a time of year that you particularly like, and take someone who you are close with, unless you just want a solitary adventure!