Most Common Non-Immigrant Work Visas:

H1B visas – most professionals seeking admission to work in the United States, seek this visa. However, there are few limitations attached to this visa. Read More on H1B visas here.
 
L1A Visas – these are intra-transferee visas allowing multi-national corporations to transfer Executive or Managerial positions employees to the United States. Note that this visa can successfully be used as an investor visa in some instances. 

L1B Visas – these are intra-transferee visas for multi-national companies who are in an specialized occupation. Read about L1B visas here.
 
TN visas – applicable to NAFTA countries like Mexico and Canada. The visa work a little like the H1B visa except the process is often easier but has many other limitations.
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O visas – The O-1 classification is divided into O-1A and O-1B sub-categories. An O-1A visa is for a worker who has extraordinary ability in the sciences, education, business, athletics, while an O-1B visa is for a worker who has extraordinary ability in the arts, motion picture, or television industry. Read more here
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Most Common Immigrant Work Visas
 
EB1(a) – It is a visa for people of Extraordinary Ability. An EB1A is an immigrant visa in the EB1 category that is reserved for foreign workers of extraordinary ability in the sciences, arts, education, business or athletics. The interesting part with an EB1A, is that it does not require an employer and the visa is available and current for all the countries of the world. Read about EB1A here
 
EB1B  or EB1-2 – An EB1B is an immigrant visa in the EB1 category that is reserved for outstanding foreign professors and researchers.
 
EB1C –  An EB1C is an immigrant visa in the EB1 category that is reserved for executives and managers transferred from a multinational corporation.
 
National Interest Waiver (NIW) – The National Interest is a very interesting EB2 category greencard for those who qualify. It is also an immigrant visa without employer requirement.
 
EB2 Categories – EB2 can be either NIW or through the labor certification process.  This is among the most common ways to obtain a greencard through employment in the United States.
 
EB3 Categories – Employment Based category 3 is also a very common way to obtain a permanent residence through employment. The process is the same as the EB2 above except the category and waiting time for a greencard is usually longer.
 
Most Common Investor Visas
 
E2 Visa – The E2 treaty visa is available to certain countries which have a treaty with the United States. It is an interesting visa for those from certain European countires, Egypt, Pakistan, Jordan, Singapore and Canada.
 
EB5 Visa – Investing $1000.000 or $500,000 to obtain a permanent residence.