My suggestion would be Python, since its a scripting language (simple syntax). Python is however not intended for large scale codes especially if speed/performance is a critical issue (C++ & FORTRAN would be much faster then).
If you want to have an idea of the speed differences between the different languages:
http://shootout.alioth.debian.org/ You can try Python's SciPy/NumPy, since the software is essentially free, and it has some close resemblance to MATLAB syntax.
If you're running Windows, then you can get Python and all the relevant packages in a single installation:
http://www.pythonxy.com
or if you're running Linux, then you need the following packages:
ipython #an improved python interpreter
python-numpy
python-scientific
python-matplotlib #provides visualization capability
Basic Python tutorial:
http://www.swaroopch.com/notes/Python (stick with python 2.x for the beginning)
SciPy: http://www.scipy.org/Getting_Started
A good & simple IDE (integrated development environment) for both Linux & Windows
is IEP:
http://code.google.com/p/iep/
Python XY already has an IDE (Spyder)