I've heard you don't need a visa to visit Thailand. I'm wondering how long you can stay before you need some sort of visa?

If you're from the United States, you don't need a tourist visa to go into Thailand. Just show up with your U.S. Passport. When you go through immigration, they will stamp your passport and write in your passport that the stamp is good for 30 days. If you need to stay longer than that, you can simply go to the embassy in Bangkok or Chiang Mai and request an extension.

Or, one time when I was there, my 30 days was up so I went across the border to Myamar for about an hour or so. When I came back into Thailand, I (near Chiang Rai) I got a new stamp good for another 30 days. However, I believe things have changes quite a bit since the coup. From what I understand...that is frowned upon now.

Peace,
Mark-N-AAm

Visa runs are what many people do. You get to see other countries doing it this way.

Yup, but the days of doing that indefinately are over, the last time I was in LOS there was a sign at the Immigration desk stating that now you may enter Thailand once every 90 days, so if you are on a 30 day tourist "pass" and you want to stay, go pay for the 90 day extended tourist visa, don't risk a visa run and get stuck in Cambodia, Laos, or Burma for 2 months waiting to get back into Thailand.