There are also other phone rings in your standard selection, like Old Phone, etc. Otherwise, there isn't anything else legal other than the songs you can turn into ringtones. Perhaps you can find a song you like and just snip a few seconds of it as your ringtone. You can do a search on google for songs taht contain phone rings inside them, and just use the phone ring, if that song is available for a ringtone. But otherwise, that is the way it is done on the iPhone without resorting to illegal hacks.