The United States Bureau of Labor does a good job tracking jobs and has publications worth taking a look at:
Occupational Outlook Handbook tells you: the training and education needed; earnings; expected job prospects; what workers do on the job; working conditions
Occupational Outlook Quarterly provides practical information on jobs and careers. Articles are written in straightforward, non-technical language and cover a wide variety of career and work-related topics such as unusual occupations, tips for jobseekers, salary trends, and results of new studies from the Bureau of Labor Statistics.
O*NET OnLine is the nation's primary source of occupational information. Central to the project is the O*NET database, containing information on hundreds of standardized and occupation-specific descriptors. The database is continually updated by surveying a broad range of workers from each occupation. Information from this database forms the heart of O*NET OnLine, an interactive application for exploring and searching occupations. The database also provides the basis for our Career Exploration Tools, a set of valuable assessment instruments for workers and students looking to find or change careers.
Bureau of Labor Statistics by Occupation program produces employment and wage estimates for over 800 occuhpations. These are estimates of the number of people employed in certain occupations, and estimates of the wages paid to them. Self-employed persons are not included in the estimates. These estimates are available for the nation as a whole, for individual States, and for metropolitan and nonmetropolitan areas; national occupational estimates for specific industries are also available.