For U.S. citizens, you can come to Thailand and stay without visa for 30 days. But if you want to stay longer you need to get a visa ahead of time. A tourist visa will be valid 90 days. After 90 days, if you want to stay more, you need to leave the country and get another visa from a Thai Embassy outside of Thailand. And now we go to Laos...
We left Bangkok around 9 pm. Our destination was Nong Khai: a border city in the North East of Thailand. We took the bus from the Air Udon company, it was quite comfortable though. The bus cost us 450 baht each (around $15).
The bus ride took around 8 hours to get to Nong Khai. We arrived at 5 am. The weather in Nong Khai at that time of the year (Jan-Feb) is always good. The temperature was around 20°c.
After we arrived at Nong Khai bus station we needed to take a tuk-tuk to the border. Tuk-tuk costs around 100 baht (around $3). From the Thai border office, there was a mini-van service to take us across the bridge to the Laos border office.
For Thais, you do not need a visa to enter to Laos, and you can stay up to 30 days. For U.S. citizens, you can get visa on arrival. It will cost you 1,500 baht (or only $35 if you pay in US dollars). You also need 1 two-inch photo for the Laos visa, and the wait is around 30 minutes if there aren't too many other people.