Separate ringtone for calls from numbers not in the contact list? Good old Siemens phones had a feature that allowed you to set a single ringtone for all calls coming from your contacts, and a single ringtone for all calls coming from numbers not in your contact list. Can it be done with stock Android 2.2, a manufacturer-specific distribution, or with an app?
Amongst the many features it lists, WhoIsIt claims to have support for separate ringtone and vibrate pattern for Unknown Callers.

See if that helps.