1st Employment Preference: "Priority Workers" -- does not require a Labor Certification
The category E-1-1 is for persons with "extraordinary ability" in arts, sciences, education, business or athletics (this is the only category in which it is not necessary to have a "sponsoring employer"). The category E-1-2 is for outstanding professors and researchers. The category E-1-3 is for multinational executives and managers.
2nd Employment Preference
The category E-2-1-A is for professionals holding advanced degrees (or bachelor's degree plus 5 years of "progressive experience"). This always requires a "Labor Certification" (PERM). The category E-2-1-B is for persons of "exceptional ability" in the sciences, arts or business -- no Labor Certification necessary if a "national interest waiver" is approved.
3rd Employment Preference (always requires a "Labor Certification")
The category E-3-1 is for skilled workers with at least 2 years of training or experience. The category E-3-2 is for professionals with baccalaureate degrees. The category E-W-3 is for "Unskilled" workers (limited to 10,000 "Green Cards" per year).
4th Employment Preference
The category S-D-1 is for ministers, religious workers and other "Special Immigrants."
5th Employment Preference
The category C-5-1 is for investors whose investment is targeted outside employment areas. The category T-5-1 is for investors whose investment is targeted in employment areas.