Unlike some 42+ countries in the world, the US does not issue the so-called Retirement Visa, aka the Silver Card. A non US citizen must have a green card (Alien Registration Card aka Form I-551) or visa if want to retire and live in the United States.
If you already have a green card, all you have to do is to maintain the validity by diligently renewing the card at the time of renewal is needed. If you have already had the green card for more than 5 years in good standing and meet all requirements, you may apply to become a citizen by the naturalization process.
For more info: http://www.uscis.gov/portal/site/uscis
If you were in the US with a work or student visa sponsored by work or school, and you are no longer working or in school, you will need to obtain another visa by doing one of the following:
1) Apply for E-2 Visa (Investor’s Visa)
In order to qualify for E-2 visa, one must have a substantial active investment, usually ranging from $100,000 to $150,000, depending on the type of business. One must prove that the business invested is lucrative enough to bring benefits to the US and the people of US through employment. E-2 visa allows up to 2 co-investors that are family members or non related investors.
Dependent children under 21 will normally receive E-2 dependent visas, which will be valid until their 21st birthday. Dependent children are not allowed to work, but are allowed to attend school or just accompany their parents until they are 21 years old, at which point they will have to qualify for visas of their own. Fore more info; http://travel.state.gov/visa/temp/types/types_1273.html
2) Apply for a Green Card (Permanent Residency)
You can apply for a green card through your family or work.
For more info: http://www.uscis.gov/portal/site/uscis
You can also enter into Diversity Immigrant Visa Program for a chance to win the Green Card by lottery. The USCIS issues 50,000 of green cards to those who were selected randomly out of the eligible countries with low rate of immigration to the US.
For more info: http://www.uscis.gov/
