- Source of online sounds like the iTunes Music Store (iTMS).
- A way to capture the sounds: Wiretap Pro, RadioLover, Audio Hijack.
- A way to convert to MP3 format (if needed), such as Amadeus II.
- A Bluetooth cell phone that plays MP3 files as ringtones.
Connect to the cell phone via Bluetooth using the Browse Devices entry under the Bluetooth menubar icon. Drag the MP3 file over to the cell phone and set it as your ring tone. For personal use, I believe this is legal :), and it is considerably cheaper than the ringtones my kids were downloading.
Of course, you can also make your own ringtones via Garageband, Reason, etc. There are probably ways to do this entire process with free software tools, but I just used what I had available, so I'll leave that for the comments.

