On my tp2 running froyo 2.2 /media/audio/notifications DID NOT WORK
I had to put notifications in root ie /notifications
once I did that those sounds became available. oddly enough once I made /notifications NOW and ONLY NOW /media/audio/notifications ALSO appear to have become available (since I now have each sound twice ??)
gmail and wootwatcher let you specify custom sounds other than "system default"
ebay and package tracking do not.
now I was able to set package tracking and ebay to their own sound "kind of"
I set my default sound to what I want them to be because MESSAGING also lets you set a custom sound.