I just bought the 'ebay toslink' (the only glass toslink sold on eBay) and I'm quite impressed with it. Significant upgrade from the cheap GE cable I was using. This cable is said to be identical to much higher priced glass toslinks on the market according to those who have compared them on AudioAsylum.
EDIT: I still have no clue why different digital cables will affect the sound. Coax I can almost understand, optical is beyond me. I just report what I hear.