This site allows you to create, upload and share original ringtones. I used it to create a ringtone for my phone using public domain music. You can also use copyrighted material to create a ringtone, but I cannot encourage this practice as it is illegal. If you want to create original ringtones, you can do it here through the web browser with no additional software. You upload the audio file to their servers, cut out about 30 seconds of it for a ringtone and then send a text message to your phone. This text message will include directions on what to do to get the ringtone on your phone. Be forewarned, you will be charged for the text message and the data download unless you have an unlimited plan.
You can also sell ringtones at Myxer so if you are looking for an interesting fundraising idea, why not sell ringtones.