[mahmud]

If you know python and ruby, learn something that I will actually improve/change your programming: Scheme, ML, Prolog, Smalltalk, Common Lisp, Haskell, Mozart/Oz, or Forth.

Python and Ruby are not that different, and neither is that different from Perl.

[mechanical_fish]

You left out Javascript and C, which are even more obvious low-hanging fruit, though not necessarily as mind-expanding.

[jrockway]

Javascript is essentially a less-functional version of Python, Perl, and Ruby -- but with many annoying bugs. (Variable scoping, for one.)

If you want to learn about prototype-based OO systems, fine, but there's a reason that only JavaScript (and Self) use prototype-based OO :P

C should be learned so that you are not tempted to ever use it for anything important.

[berntb]

The first time in my life I bought a book for looks, was when I saw how thin "JavaScript: The Good Parts" was. :-)

Disclaimer: I quite like JavaScript.