Hi All:  I'm a 55 year old man in the USA and want to retire to Thailand.  What is the best visa for me to get.  Your help and advice is appreciated.  

Read the post to Tonto a few minutes ago for information on retirement visa, which is what you probably want.

You apply for a non-immigrant O visa for the purposes of retirement in Thailand.  http://www.thaivisa.com/275.0.html.  You should get a 90 day visa.  

Within 90 days report to immigration and ask for a one year extension for retirement purposes.  

You will need to transfer (not carry with you) B800,000 to a thai bank, from a legitimate source, like a bank in your home country or, if you are on a pension you will need proof of retirement pay of at least Baht 65,000 per month and no bank deposit will be required, buut you will need to open a local bank account and make monthly transfers to prove that you are bringing the money in and not making it here, as on a retirement visa you are not legally allowed to work here.  Immigration has been using the exchange rate of B40= US$1, but check with the Thai Embassy or one of the consulates in the USA to be sure.  

If your retirement pay is less than B65000 per month, then you will need a combination of the lump sum deposit and monthly income.  The way to calculate this is to take the monthly pension amount, say B50,000 and multiply it by 12, which is B600,000.  Then subtract that amount from B800,000.  The remaining amount (B200,000 in this example) is the amount you will need to deposit as a lump sum by transfer from  the USA (if that is where you keep your money), after you arrive here.  You can use the lump sum after you get your visa extension, but each year before renewing your retirement visa, you will have to to show that you have the B200,000 in the bank in addition to your monthly pension transfers.