In Spain "that's cool" is: "mola", "está guay", "está chulo"... and "that sounds cool" could be something like "suena bien", "suena genial", "suena guay", "suena chulo"....

the best answer is from nightmary, to spanish people.

Se dice sin mucho formalismo " ESTA PADRE o PADRISIMO" o un poco mas callejero " ESTA CHIDO"

en chile: Es BAKÁN, GENIAL, FILETE, pero.. en general se usa: ES GENIAL

yo diria simplemente: chido!!