From xilisoft.com:

Xilisoft iPhone Ringtone Maker for Mac lets you convert favorite music/ songs in WMA, WAV, RA, M4A, MP3 formats to M4R iPhone ringtones. Also, it can convert AVI, WMV, DivX, MP4, H.264/AVC, AVCHD, MKV, RM, MOV, XviD, 3GP, and MPEG to M4R for making background music as your iPhone ringtone.
Furthermore, with Xilisoft iPhone Ringtone Maker for Mac, you can also create ringtone clip from any video/audio and turn it into iPhone ringtone. Only a video and an audio file are needed and all the rest Xilisoft iPhone Ringtone Maker for Mac will automatically do.

Key features:
1. Customize iPhone ringtone on Mac by selecting exactly the part of the music or song you want to convert.
2. Transfer ringtones to your iPhone directly and set as iPhone ringtone after iPhone ringtone creation is done.
3. Enjoy ringtone melody beforehand with the built-in player.
4. No matter MP3 to iPhone ringtone or AVI to iPhone ringtone conversion, all of the video/audio to ringtone conversion is faster than you can expect.
5. The ringtone software provides several interface languages to choose: English, German, Japanese and Chinese.

Xilisoft Corporation is dedicating to digital video and audio software developing and user experience to bring users the most excellent software and technology all the while.