Ringtone Maker Pro.....Have any of your music as a tone, works on the iPad too...I think I paid 69p or 30c for it...Never bought a ringtone in my life...far to mean....
I will create them on iTunes setting the start and stop point of a song/sound file then convert it. I convert them to a single channel 128kps file since they are smaller and going higher or better does nothing to improve the sound over the phone speakers.
Now if I want it to be really exact I will open the file in garage band and set it up that way to get the exactly where I can see the wave pattern and get it exactly where I want it as I did with my current one but it is not very often that I need to be that exact.
you could try zedge.net and mytinyphone.com because its a great way to get and make your own ringtones by uploading them as like i do usually and on the otherhand if you have all the songs on your computer that you want to make into ringtones then try ventones.com,Good luck.