I know where you can get free ringtones for the Nokia 5185 (that's what I have). While there's no composer on the phone, if you go to www.2thumbswap.com they have free cell phone ring tones. I thought they had Siemens, too, but I can't quite remember.
Anyways, for the Nokia ones, you have to have text messaging available on your phone. Not all of the rings work just yet, as they admit, since it's still in beta testing. Still, you can get a few good ones off there!
-Kirsten