use myxer.com - you can get free and/or cheap ring tones, or upload your own mp3 and the site will send it as a txt message to your phone. for free! (I was happy because you don't even need to create an account to use this service.) when you get the txt message from them, you hit "save" and the sound will end up in your list of ring tones.

fyi: I found a really loud ringtone on myxer called "annoying beeps". yes, it is annoying, but it is so loud, if you're outside walking around in a city, you should be able to hear it!

note: before you send a ringtone to your phone, you can edit it a bit. choose the "customize it first"  button, and you can edit the volume, length of time the song is, etc. choosing "loudest" on the volume really helped.