A request on HoFo for an application to play random ringtones from a selected library was posted. I busted out some google-fu and turned on FreeTones which is a freeware application that does just that. I wasn't able to find the developers homepage so I have attached it here. I ran through a quick once over of the application and it works perfectly. Once started up, you are greeted with the Settings menu;
You will first need to enable it and if you so choose, enable auto-boot so it starts up when your device starts up.
You then move onto the Call Settings where you can set the application to play randomly. FreeTones can also play random tones for an incoming SMS. I didn't bother with this part as I like to keep a short discreet tone.
Tones are easily added by selecting them and pushing "Add" to the library, so you can select from a set of specific tones to play. Upon the first call, you regular ringtone will be used - after that Freetones will kick it and play a random tone as it is supposed to do. It takes up very little memory, so no worries about slowing down your device running this.
Again, since I was unable to find the homepage I have uploaded the newest version to Mosh.