[RdBrd83]

Since I made the Android switch I've been using Ringdroid to trim my mp3 files. It gives the option to save as an alarm, notification, or ringtone.. Then it will show up in the stock selection lists.
Other than that, I'm not sure, because the sounds are in /system/media/audio, then there is alarms, notification, and ringtone folders. However the only way to get to that is to be rooted. And adding files there is probably more of a pain than just using the music library.