Delta Connection flight numbers:

Flights 800-839 Northwest - NW
Flights 850-947 Pinnacle - 9E
Flights 950-999, Mesaba - XJ
Flights 4415-4934, SkyWest Airlines - OO
Flights 4939-5651, ASA - EV
Flights 5875-5884 Compass Airlines - CP
Flights 5900-5991 Shuttle America - S5
Flights 6001-6094 Chautauqua Airlines - RP
Flights 6100-6214 Freedom Airlines - F8
Flights 6225-6776 COMAIR - OH

SkyTeam (and other) codeshares:

Flights 2365-4364, 6801-6827 Northwest - NW
Flights 6970-6983 China Airlines- CI
Flights 7400-7467 American Airlines - AA
Flights 7550-7812 SkyWest Airlines - OO
Flights 7650-7708, 8992-9124 Alaska Airlines - AS
Flights 7725-7751 US Helicopter - UH
Flights 7815-7837 China Southern - CZ
Flights 7840-7849 Royal Air Maroc - AT
Flights 7850-7937 Korean Air - KE
Flights 8005-8119 Aeromexico - AM
Flights 8120-8219 Alitalia - AZ
Flights 8320-8709 Air France - AF
Flights 8710-8759 Czech Airlines - OK
Flights 8770-8891, 9275-9379 KLM - KL
Flights 9665-9683 AVIANCA - AV

Oddly enough, OO flights aren't classified as DCI flights.