These are the two they use most often. When they have an emergency situation on ch1 (TG 30366), the other units will continue regular dispatch on ch2 (TG 30367).
30366 Normal Police: Dispatch
30367 Normal Police: Channel 2 - Car-to-Car
I've heard 453.950 (103.5), old NPD 2, used in the last few weeks by what sounds like the Park District. Sometimes you will hear an ISU unit key-up on 458.900 (103.5) which can accidentally activate the 453.950 repeater. I haven't heard anything on 460.025 since NPD switched to Starcom21 in Feb 2006.