Some things may have changed since you left the language, here some personal proposals:
- Servlets and JSP, you should take the dust off to this and include some EL (Expression Language)
- A build tool (Maven or Ant), most of Java application are now built with the help of them.
- Any Web Framework (Spring MVC, Struts2 or JSF are good choices)
- IoC and ORM (Spring and Hibernate are good choices)
- Take a look to Apache Commons and use them when possible
Also some features from Java 5+ like:
