These are for temporary stays in the U.S.
B-1: Business visitors
B-2: Tourism, vacation, and visiting
H-1B: Specialty occupations
H-2A: Seasonal agricultural workers
H-3: Trainees other than medical or academic
L-1: Intra-company transferees
O-1: Individuals with extraordinary ability or achievement
P-1: Athletes, artists, and entertainers
Q-1: Participants in international cultural exchange programs
F-1: Academic students
M-1: Vocational students
J-1: Exchange visitors
C: Transit through the U.S.
D: Crew members on ships and aircraft
R-1: Religious workers
I: Representatives of foreign media
These are for those intending to live permanently in the U.S.
IR1/CR1: Spouse of a U.S. citizen
IR2/CR2: Unmarried child under 21 years of age of a U.S. citizen
IR3/IR4: Orphan adopted abroad by a U.S. citizen / Orphan to be adopted in the U.S. by a U.S. citizen
IR5: Parent of a U.S. citizen who is at least 21 years old
F1: Unmarried sons and daughters of U.S. citizens
F2A: Spouses and children of permanent residents
F2B: Unmarried sons and daughters (21 years or older) of permanent residents
F3: Married sons and daughters of U.S. citizens
F4: Brothers and sisters of U.S. citizens
EB-1: Priority workers, including individuals with extraordinary abilities, outstanding professors and researchers, and certain multinational executives and managers
EB-2: Professionals holding advanced degrees and individuals with exceptional ability
EB-3: Skilled workers, professionals, and other workers
EB-4: Special immigrants, including certain religious workers, employees of U.S. foreign service posts, and others
EB-5: Immigrant investors
DV: For individuals from countries with historically low rates of immigration to the U.S. (commonly known as the "Green Card Lottery")
SI: Iraqi and Afghan translators/interpreters
SQ: Certain Iraqi and Afghan nationals who worked for/on behalf of the U.S. government
If you need detailed information on a specific visa type or have any particular questions, feel free to ask!