stack based languages

Hello, i am interested in learning a stack oriented language, so i started learning Forth. (from http://www.amresearch.com/starting_forth/)
Some alternatives i heard of are cat and factor.

What is best to learn from those? And suggest a good tutorial

[/code]: fib ( n -- result ) dup zero? [ 1 ] [ 1- dup fib 1- fib + ] if ;[/code]

much nicer than >>29