+1 Python. Write first, optimize later (if at all) using Cython or separate C packages. I'm also keeping an eye on the Nim language; it's still too buggy for real use, though.
I used to use the Enthought python distribution, but it's become too complicated. I've now moved to compiling and installing python through homebrew on my Mac, and then installing the python packages from the pypi repository. I highly recommend using homebrew for anything you want to run from the command line.
For Windows boxes, I've been installing Anaconda Python.
As for IDE, I've been very happy with the eclipse-based Aptana Studio 3, with pydev. I still use VIM for small scripts, but the features provided by pydev, such as refactoring, are very handy for larger projects.