Employment Pass - For company owners or skilled employees that will be working in Singapore. Your fixed monthly salary must be more than S$2,500 and you should be a degree holder from a reputable university. There is no official quota system limiting the number of Employment Passes that can be issued.
Entrepreneur Pass - Is a variation of Employment Pass and is meant for entrepreneurs wishing to start a business in Singapore who might not qualify under Employment Pass category due to the lack of education qualifications.
S Pass - For mid-skilled employees who earn a fixed monthly salary of at least $1,800. S Pass applicants are assessed based on employer's quota eligibility and applicant's qualifications. Instead of a degree, a technical diploma is acceptable for this kind of work pass.
Personalised Employment Pass (PEP) - Is a special type of Employment Pass that is not tied to a specific employer. The biggest benefit of having a PEP work permit is that you can switch jobs without re-applying for a new employment pass provided that you are not unemployed for more than six months. Candidates must meet specific requirements before a PEP is approved.
And then of course there are other passes like the Miscellaneous Work Pass, Training Employment Pass, Employment Pass Eligibility Certificate etc.