There is. Create a folder called media on the root of your SD card, then create folders called notifications and ringtones inside it (all folder names in lower case)
Placing your music/sounds in there will add them to Android's list of ringtones/notification sounds so you can choose your desired notification sound.
Samsung Galaxy Nexus @ CyanogenMod 9 Nightlies (Android 4.0.4)
ASUS EeePad Transformer Prime @ stock (Android 4.0.3)
HTC Desire Z @ CyanogenMod 9 RC0 (Android 4.0.4)
HTC Flyer @ LeeDrOiD HC (Android 3.2.1)