The Bureau of Labor Statistics has employment projections for a vast number of occupations at http://www.bls.gov/emp/ep_table_102.htm. These projections are based on a huge amount of data and analysis, and, so, should be good indicators. In not all, but a great many, cases, the major to have for an occupation is obvious. And average pay for various occupations is at http://www.bls.gov/oes/current/oes_nat.htm .