I'm going to Costa Rica for my birthday, 12/26 - 1/2. I've never been there and I'm just beginning my research. I'm not even sure what city/town to fly into. As usual, I'm traveling solo. I welcome any tips/hints/recs for Costa Rica.

San Jose has the international airport. Liberia has the secondary airport.
From the US you will most likely fly into SJO. Unless you depart from a US airport on one of the Latin American airlines that serve Liberia.
San Jose is in the central valley and is generally the starting point for most tourists. From their you choose what region you want by the type of experience you desire.
A couple of websites that were very helpful to us were:
http://www.centralamerica.com
and the fodors travel talk boards. Fodors has a good amount of posts and helpful posters on Costa Rica.
http://www.fodors.com

Actually, Liberia has many flights directly from the US. Delta and I believe Continental and American all have daily flights there. Which airport you fly into would depend on where you want to go after you arrive. If you want to head south toward Manuel Antonio or the Osa Peninsula, or east toward the Caribbean side, you should fly into San Jose. If you want to head north in Guanacaste or to the Nicoya Peninsula, Liberia would be a better choice. Arenal and Monteverde are about equally distant from both, although it is much easier to arrange ground transport from San Jose if you don't rent a car.

I just re-read your post and saw that you are intending to travel to CR during Christmas week. I don't want to discourage you, but Christmas week is one of the two busiest vacation weeks for native Ticos. Many Ticos book their hotels months in advance for this week. Consequently, rooms are at a premium. You would be much better off waiting until after New Year's if possible. If you must travel during Christmas week, I suggest you get busy right now trying to find rooms. I wouldn't wing it.

I want to make arrangements right away, but I don't even know where to stay.

I am a city-girl. I'm not so much into hiking through beautiful mountains as I am meeting new people in cities. I would like to get in a beach day or two. I would like to dive or snorkle, but mostly I want to enjoy my birthday and New Years in nice clubs and restaurants. I would also like to see the archeological site, which I cannot remember the name of at the moment (I'll post it when I get home from work).

Can anyone recommend areas, hotels, a basic itinerary?

I happen to love Costa Rica - I've been there three times in the past three years. But I'm not sure it's the destination you are looking for. It is not a "city" kind of place. The largest city, San Jose, has a few museums and a couple of restaurants and clubs, but it won't make anyone forget about Paris or Rome. Most people use San Jose (or nearby Alejuela) as a place to spend the night of arrival or the night before departure, but not as a destination itself. The other cities (Cartago, Liberia and Limon) do not hold much attraction for tourists. The attraction of Costa Rica is its natural beauty: the cloud forests, the volcanoes and the beaches. Most visitors try to see either Arenal Volcano or Monteverde Cloud Forest (or both), and a beach destination (Manuel Antonio or somewhere on the Nicoya Peninsula.) I just came back from the Caribbean Coast, which I thought was beautiful.Where you go would depend in part on how you intend to travel (i.e rent a car or take public transportation.) I saw that you found the Costa Rica forum on Fodors. That is an extremely helpful resource. I also suggest you look at Let's Go.com.
Here are some useful links:

http://www.costarica.org/

http://www.costaricabureau.com/

http://www.caribbean-on-line.com/islands/ca/camap.shtml

http://www.letsgo.com/CORI/00-Discover-1

http://www.lonelyplanet.com/destinations/central_america/costa_rica/

Thanks.

I think that I have to re-think Costa Rica. I'm learning that to really enjoy the trip, I'll have to plan it out farther in advance. Plus airfare is still $1100. Yuck.

So, this leaves the question... Where should I go for my birthday? I'm considering Mexico. Any thoughts?

Changed my mind.

I'm going to Tokyo instead

If you change your plans again and end up in Miami let me know. I will be there December 29 to January 2.

Miss Eve, you may want to consider a US destination.
My daughter and her husband had a birthday trip planned to Key West for mid-September. A couple of weather bullies kept them from going.
Now they are going in mid-December instead and tell me they have found some fantastic bargains. Key West was not harmed by the hurricanes physically, but the tourism was wiped out. So there are a lot of discount offers.

Kelly - please email me: mizzeve@earthlink.net