Hey dear, from your question it can be assumed that you are asking about placements of engineering, mba e.t.c. so, there are many companies that visit colleges for placements like infosys and wipro are mass recuiters in many colleges. Then come some majot core companies those are limited to certain branches, that too are regular companies visiting every year in colleges. For MBA, companies like accenture, TCS come for management sector in most  of the colleges.