Android: You don’t have to lose custom ringtone identifiers just because your phone is on vibrate. ViBe sets specific vibration patterns for specific callers.
ViBe comes packaged with 10 ViBes (the vibration equivalent of a ringtone), the first 5 are available in the free edition and the remaining 5 are unlocked via premium upgrade ($4 to unlock all 5). The free selections include Knock Knock, Ramp Down, Bee, Heartbeat, and Crash.
One welcome feature, even if it was restricted to the premium edition, would be a built-in tool for creating your own vibration patterns.
ViBe is free, requires Android 2.1+.