There are many softwares out on the market to create ringtones. Most of them are difficult to use, and then they can not create the ringtones for the iphone directly and you have to convert them first.
The easy way to create and/or download new ringtones is to go to audiko.net. Either you can use the search function on the homepage and download the ringtone directly (you can download it in mp3-format or directly as a m4r-ringtone for use with the iphone). There are already loads of ringtones available, all created by other users, and before downloading, it is possible to listen to them.

However, to create a ringtone from a mp3-file, just follow this easy steps:

1. Choose your song and upload it (takes about 2-4 minutes, depends on your bandwidth)
2. Once uploaded, use the flash interface to choose the part of the song which should become your ringtone.
3. Click on “Create Ringtone” to start creating ringtone
4. Input the songs name, once done, you can download it either as a mp3 or m4r

That’s it! Easy, no?