I’m a single guy planning my first “real” non-family vacation, and I want to get suggestions. 
I grew up in the US and the only countries I’ve been to outside of it are in the Caribbean, so my options for “new places” are very open.
I have a bunch of airline miles saved up, so tell me: What country should I visit, and what makes that a better place to go than all those other countries out there? 
Are you going alone?
At the moment, yes.
Go on a safari to Kenya. See the Serengeti.
Three questions you should ask yourself:
(1) What are you interests? Museums, nature, partying, etc.?
(2) How comfortable would you be in a place where people mostly don’t speak English?
(3) How comfortable are you with foreign foods, customs, etc.?
What are you looking to do on this vacation? Is it a bikini watch, for scenic vistas, locales of historic significance, to bike, swim and climb, or some combination thereof? Do you want places with a strong cultural influence, is English-speaking important? Give us some clues as to what might float your boat.
Outdoor activities are probably my primary interest, but cultural stuff is cool by me as well. Not much of a partier, sadly.
Semi-comfortable, I enjoy learning new languages. I’d definitely want to pick someplace where I could learn the basics of the language before I went, assuming English wasn’t usable.
I’m a bit of a picky eater, but I can deal as long as I’m not eating animal brains or grubs or something 
In terms of learning customs, no problem on my part, I’d just consider it a part of the cultural experience.
Are you more comfortable at 10,000 feet above sea level, or 0 feet above sea level?
Would you rather eat steak or lobster?
Would you rather walk through the woods or quaint shops?
How important is weather/season to you?
Being a west coaster and relatively near, New Zealand offers some of the best scenery on the planet. Have you the time, you could then hop over to Australia and a huge door of possibilities opens up. Western Canada, specifically the mountains of BC offer world class activities in winter or summer. Alaska is spectacular in the summer, especially down the Kenai Peninsula.
So the safari doesn’t sound like a good vacation to you?
(I’m planning my 3-week trip to Kenya for the spring of 2010)
Thailand has a lot to offer, plus you can use it as a springboard for other destinations. Angkor Wat in Cambodia is awesome.
How much time and money do you have? My theory is that if you haven’t done much overseas travel, it’s best to start out easy and then work your way up to more exotic locales. New Zealand, Australia, England, Ireland and Scotland are all English speaking countries that are damn interesting to visit, and have super great tourist infrastructure. All of these places have tremendous natural beauty. And in England (Cockney accent) or in the boonies of Ireland or Scotland, you won’t be able to understand a damn word some people are saying anyhow (Think Brad Pitt in Snatch).
I’m completely in favor of low budget travel. Staying in inexpensive hostels is a fantastic way to meet people, you just have to be able to tolerate a lot of noise and drunken people.
In Western Europe, you will almost always be able to find someone who speaks English. In Amsterdam, almost everybody speaks English. I find the French to be less willing to try to understand an English speaking person than any other country I’ve ever been to. In my experience, a lot of Parisians deserve their snobby reputations.
I wouldn’t go to southeast Asia until I had a bit more traveling experience under my belt. It is wonderful and inexpensive, but a much more challenging environment than western Europe.
Going on safari in Africa was one of the most thrilling things I’ve done in my life. Keep in mind, South Africa is about a billion miles away (usually 3 flights and around 18 hours) from California.
The other bit of advice is if you are going outside of the Western Hemisphere, try to take at least two weeks, otherwise you’ll be fighting jet lag most of the time. If you can afford it, take off 2 or 3 months and travel to one continent. You will have the rest of your life to work.
Costa Rica has:
Great hiking and natural stuff to see like volcanoes.
Very easy for tourists. Everyone takes dollars. Tourist shuttles run between all the tourist locations.
Spanish helps, but you can get by with English.
Cuisine is mostly rice and beans and fruit.
I thought it was a very easy place to be a single backpacker.
Seconding NewZealand here. If you’re into hiking, picture-postcard views, etc., focus on the South Island. Queenstown is/was the epicenter of high adventure tourism - supposedly (for instance) bungee jumping was invented there.
Also, Tasmania (the island state at the south of Australia) could appeal to your outdoorsy tendencies. Not as picturesque as the South Island, but perhaps more interesting in terms of flora and fauna.
Both islands have multi-day hiking opportunities: The South Island’s Milford Track and Tasmania’s Overland Track being perhaps the best-known examples.
Another vote for New Zealand and Oz. The exchange rate has gone up, but it’s still favorable. Once you get used to it, driving becomes a pleasure down under. There are some incredibly scenic, well-maintained roadways along the coast, through mountains and forests – dotted with towns and villages that seem like they’re from the 50’s or 60’s. And the friendliest folks you’d ever want to meet, Some of the finest road-tripping I’ve ever done.
Thanks for all of the suggestions guys! I had thought about New Zealand as a possibility before, but now I think I’ll look into it a bit deeper. 
Seconded. Plus, if you like outdoor activities, you’ll rarely have more fun than on CR’s zip lines. Up in the treetops, zooming over valleys and forests – it’s a blast.
I’ll jump in and recommend Cancun, Mexico. Lots of beaches, so if bikini watching is what you want to do there are plenty of opportunities. Plus from there it’s very easy to get to the interior of the Yucatan penninsula. More Mayan Ruins than you can shake a stick out, pleanty of water activities along the cost. My wife and I have been to Cancun 3 times, and each time did totally different activities. The last trip we actually rented a car and drove from Cancun to Acapulco…lot of fun.
Not that you asked this, but. . .how much of the US have you seen?
Have you seen Bryce? Acadia? Hawaii?
Have you vistied New York? DC?
I know plenty of people who have been to some exotic locales and overlooked stuff that people come HERE to see.
Anyway. . .I’ve been twice to Interlaken, Switzerland. I love that place, and we’ll go back some day. AWESOME hiking and sightseeing. You can rent a car, and travel into France or Italy. Food isn’t great.
I like Paris, eastern Europe. That’s getting expensive now, though.
It looks like we might be going to Cape Town later this year. There’s swimming, hiking, safari you can do from there.
For folks suggesting New Zealand, how do you get there? What airline do you take, and how long of a flight is it from L.A. or the West Coast?