I have been asked by many people what I suggest doing in Thailand. So here you go. To anyone going to Thailand, this is what I recommend doing:
Learning about the best places in Thailand really depends on what part of Thailand you plan on visiting and what it is you want to do. So first, I suggestion picking up a Lonely Planet travel guide. I have found that to be the best the guides. You can expect the exchange rate to fluctuate between 26 -22 baht to 1 USD. Not quite sure where it stands today. One word of caution, avoid the government sponsored tourist agencies (Tourism Agency of Thailand aka TAT). They over charge for everything (nearly 80%) and don't guarantee what they offer. If you are wanting to set those types of trips they set up; such as elephant rides/visits, canoe trips, indigenous village tours, etc... it's better to go directly to the companies that are offering the tours. Your best bet, when arriving in Bangkok, is going to Khaosan Road (the travel/tourist section of Bangkok), and simply striking up a conversion with the hostel owners and other visitors there. Traveling throughout Thailand is really easy. I suggest taking overnight sleeper trains. Simply go to the train station because they have people there that speak English to help you get where you want. And it is cheaper than buying from the hotels/hostels or the TAT, hostel owners are very helpful too.
There are a few places I recommend visiting:
Of course, you will be seeing Bangkok. That is where the international flights fly into. It is crazy, hectic, loud, and has an amazing night life (mostly around the Khaoson Road area). You will be tempted to spend all your money and time in this amazingly wild place - do not do it! There is so much more. Do, however, take the orange flagged boat taxis up and down the river, visit the palace and some of the temples, and eat anything crazy and exotic you find. They are usually good. Oh, and to see most temples you will need to have either long pants or a long skirt and they frown on sleeveless shirts... don't worry that goes for men as well.
Chang Mai is a must. Be sure to be there during the weekend markets, and rent a scooter to drive up the mountains! It is absolutely BEAUTIFUL!!! And if you are thinking about getting custom dresses or clothing Chang Mai is the best place to do it. I recommend a gentleman named Mr. Somboon. He owns a shop called S.B. Tailor in the old city. His e-mail is email@example.com. He is wonderful, funny, and very very good. Just an idea of the cost: I got 2 full suits and 5 shirts for under $200ish USD. All custom made and my girlfriend got a beautiful silk dress, 2 suits, 1 skirt and shirts for about $250 USD. That was a little over a year ago.
Kanchanaburi (romanized in many different ways) is the same location as the WWII story Bridge Over the River Kwai. It's a charming and beautiful little town. But the real treasure is what they call the 7 tiered waterfalls of Erawan National Park. Be careful of food and valuables though. The monkeys will steal it and throw them down from the trees!!! The water is the most beautiful I've ever seen anywhere in the world, and you can swim in it. The only problem is getting there. You can take a tourist bus, but again, I recommend renting a scooter and driving there. It's a beautiful drive though a bit long. It makes for a great day trip. Suggestion: find a travel buddy at the hostels or on the train.
Sukhothai and Ayutthaya are two ancient temples that you must go see. Sukhothai was probably my favorite temple to visit. much of it was destroyed during the many invasions, but the parts that remain are beautiful. On my first trip to Thailand, I visited Ayutthaya. It is still a fully functioning city with remnants of the ancient Ayutthaya temple everywhere. Although it is a bit better preserved than Sukhothai, I recommend this as a day trip on the trains from Bangkok rather than staying over night. To get here, take the train. Then you'll walk a very short distance to a small ferry (fits maybe 10 people and a few bicycles). This ferry takes you across the ancient moat which is only a stones throw wide... it isn't recommended to try and swim across it.
Pai is a very tiny little village in northern Thailand past Chang Mai and only accessible by bus. The only reason I would recommend this place is because it is rustic, tiny and quiet... unlike most places you'll probably see. There are amazing food/bar places. One such place is the Bamboo bar off the river and built partially over the water. Everything here is walkable and very safe. The other reason I recommend Pai is because it is the only place I found that allows you to go from one city to another using the scooters. So when going to Chang Mai, see if there is a hostel that will let you stow your luggage there while you go to Pai. Catch the bus to Pai and scooter back to Chang Mai. It was the best part of my third visit to Thailand (and the best part for my two other friends who did that drive as well). It is about a three hour scooter ride, with sweeping views of mountains and jungles, and small villages. One down side of Pai is because it is so small, tourism is Pai's main source of income. You'll find that the night life is very tourist centered.
Finally, if you are looking for beaches, Thailand has some of the most beautiful beaches in the world. I have only been to the east coast beaches of Thailand. Here the water tends to be calmer and less visited by tourists. Chumphon is a beach protected by the King, and has probably the most beautiful sand and relaxing atmosphere I've ever experienced. However, Phuket is supposed to be very nice but heavily visited. There are beaches and islands near there that are stunning and are typically the source of beach photos on tourist web sites. These other places are harder to get to but much calmer than Phuket.