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

much nicer than >>8:
: (fib) ( result next n -- result ) 2dup zero? [ 3drop ] [ roll + swap 1- (fib) ] if ;
: fib ( n -- result ) 0 1 rot (fib) ;