1. Online advertisements is a good indication as to what skills are in demand. Go through the online advertisements.
2. http://www.google.com/trends. type in the technology and select the region to USA, and click the search button. You can search on Java programming, JEE, JSF, Spring Framework, Hibernate framework, EJB3, etc.
3. Constantly follow the industry websites like JavaLobby, The Server Side, etc to see where the industry is heading.