On the all time, top five list of destination cities in the United States, one you MUST add to your solo travel list is one that may not be so obvious for a solo-friendly excursion: Las Vegas.
Now, I know what you're thinking. Vegas is gambling, shows, buffets, more gambling, lights and attractions. But really, Vegas is probably one of the most solo-friendly destinations around, and you owe it to yourself to make the trip.
First, flights to Las Vegas are generally a pretty good deal if you shop around a little, and if you book a hotel on the Strip, you're in the middle of everything you could possibly want to do and everywhere you could possibly want to see. Check out sites like Travelocity.com or Expedia.com for great packages. You can also search Kayak.com for deals. They'll compare vacation packages for you and find some of the best on the internet.
Second, Vegas is a normal city with normal people from sun up til sundown, and after sundown, it's a fantastic place to people watch. You don't stick out when you're solo in Vegas. There are people everywhere. Just dive in. Make sure that you put the fountain at the Bellagio on your list. It's a must-see.
Third, getting into things can be easier when you're traveling solo. From shows to restaurants to clubs, going in alone can be much easier (and cheaper) than trying to get into a great club with a group of people.
Fourth, when you're gambling, the drinks are free. Always tip your cocktail waitresses.
Fifth, you can take Celebrity Las Vegas' Night Tour straight from your hotel. Champagne toast kicks off the ride and you get to meet other tourists who are out and about - you never know who you'll run into.
Plus, we all know, "what happens in Vegas stays in Vegas." So what better place to go alone? You have no witnesses.