I highly suggest buying the "Ringtone Expressions" from the crackberry store. It is like 5 bucks or something for a year subscription and it is great. Any song that I have on my iTunes, I can change into a ringtone.
A potential issue. If you select ringtones or alarms for use and they are located on the SD card and you have MassStorageMode ON, when plugged into the usb, those tunes will not work as the sd card is hidden in that case. I have moved my alarm tune to internal memory so that it works even if the usb is plugged in (charging overnight for instance). Also, if you choose your own wallpaper from the sd card, again, it will not show if you reboot attached to the usb port - I also moved that to the internal memory.
why pay for a ringtone You can also sync your own music and make it a ringtone
there are free ringtones on this site there are free sites tonzr.com is a great site and completely free