Squeak Smalltalk: almost as good as Lisp for experimental programming
I am not that good at programming Smalltalk (off and on since 1986 - mostly off). That said, I find that Squeak Smalltalk (free and open source) is a great environment for algorithm development and generally for experimentation. In the last few years, I have used Squeak (and for a year when I was a Cincom VAR, VisualWorks Smalltalk) for natural language processing.
Smalltalk is an image based system - when you start up Squeak, your working environment, including data in memory, code changes, etc. is exactly the way you left it the last time you ran the Squeak system (assuming that you save your working image).
Smalltalk is not for everyone, but it is worth a try. There are enough Squeak tutorials on the web, so at least initially, spending a few evenings with Squeak will not cost you any money.