Here's a little tutorial for you, so you can free ringtones for your iPhone or using songs from iTunes and songs you already have on your computer.
This is the way to create an iPhone ringtone using iTunes:
1. Choose a song you like and right click on it. Select "Get Info."
2. Go to the Options tab and go down to the Start Time and Stop Time check boxes. Here you have to check both boxes and then input the time you want your ringtone to start/stop. It is important that you remember your ringtone has to be 30 seconds or less. Once you're done, click OK.
3. Right click on your new "ringtone" and select Create AAC Version. Now the song will be re-encoded using the start and stop times specified.
4. Once the song is done encoding, go to your iTunes Music folder, find your song, and drag it to your desktop. Once the song is on your desktop go back to iTunes and delete the clipped version from you iTunes library.
5. Right click your song on your desktop and choose "Properties". Go to the name and extension section and change the extension from .m4a to .m4r. You can also do this step directly in your desktop.
6. The final step is to simply double click on the file. It will automatically go to your iTunes library under the ringtones section. Now just sync your iPhone with iTunes and that's it!
I hope you find this tutorial useful.