Programming Languages
At a minimum, a programmer needs to have a complete understanding of at least one (more is preferable) of the major programming languages. According to TIOBE's "Programming Community Index for September 2010," the top five most popular programming languages are Java, C, C++, PHP, and Visual Basic. Since the popularity of programming languages is constantly changing, employers look for programmers who have not only subject matter expertise in at least one of these major programming languages, but also a broad knowledge and understanding of multiple other languages such as Python, JavaScript, Ruby on Rails, C#, and so forth.
A visit to the TIOBE website or a simple Google search can put you in the know as to what programming languages are currently "hot." Programmers are expected to understand all of the nuances related to the programming languages they know. This means understanding how to architect, design, implement, test, debug, and maintain both simple and complex systems.