From Ringtone Download:
Ringtone Downloader lets you download one of 1 000 000 high quality and popular ringtones. The program makes the process just about as quick and painless as possible and it works for just about any phone you can think of. Software is just about as easy as they come: enter a song title or artist name and press the "Search" button, choose the output format you want, either .M4R for use with iPhone or .MP3 and select a ringtone to download by clicking on the "Download" button. It supports the iPhone, Android, BlackBerry, Windows Phone, and more. In seconds, you'll have a fully functional ringtone you can put on your device and assign to incoming calls.