Everyone says C which is a great language but realistically it depends highly on what kind of job you end up with and what your interests are. The vast majority of jobs occupied by EEs do not require C programming skills. C programming is pretty specific to working in embedded devices.
Python is an excellent general purpose language. I highly recommend it regardless of your interests and ambitions.
Excel VBA will be useful in almost any job.
On top of these, it highly depends on your interests and ambitions.
C, C++ - Embedded
C, C++, Python, Matlab, Fortran - Scientific computing, Analog, DSP, RF
ASM - Almost useless in practice, important to understand though
Ruby, Python, Javascript, CSS, HTML - WebDev (more software engineering esque)
R - Statistics
But overall, the language you learn isn't necessarily that important. It is more valuable to have deep knowledge about what to tell computers to do, not how to tell them to do it. What I mean, is that it is better to know a lot about implementation strategies (how to work with threads/processes and when/when not to use them, how to manage shared memory, how to work with an operating system...), algorithms (how to apply algorithms, not necessarily how to write them), design methods (UML!), etc..
For example, it is far better to know how to design a driver for a new type of sensor than it is to know every possible "pointer hack" in C. And, it is better to know what methods you need to apply to a certain data set than to know everything there is to know about list comprehensions in Python.
Ultimately, when it comes to languages, you should learn only as much as is necessary to implement your solution to a problem. The language is not the solution, it is only the tool you use to implement it.