SDP45:
Road names include Erie Lackawanna, Union Pacific, Conrail, Burlington Northern, Great Northern, and many Southern Pacific paint schemes.
SD45-2:
Road Names include Santa Fe, Clinchfield, Seaboard Coast Line, Erie Lackawanna, BNSF, Norfolk Southern, Conrail, CSX, MRL.
MTH offered their rendition of this locomotive, but it was actually just an SD45 painted like a Dash 2.
Various EMD Widecab units:
SD60M "Triclops":
Roadnames include Burlington Northern, Union Pacific, Soo Line, Canadian Pacific, BNSF, Norfolk Southern.
SD60I:
Roadnames include Conrail, Norfolk Southern and CSX.
All that would be needed to make this engine in O scale would be a die insert to make the gasket for the I cab, the rest of the engine is identical to an SD60M.
SD70I/SD75I:
Roadnames include CN, BNSF, Santa Fe, and now Norfolk Southern.
This engine falls into the same scenario that the SD60I does, all MTH has to do to make this engine is put an I cab gasket on the SD70M.
SD70MAC: (not a fake one like Lionel and MTH)
Roadnames include BNSF, Burlington Northern, Conrail, KCS, TFM, and CSX.
While both Lionel and MTH have produced an SD70MAC, the Lionel one is actually and SD60M and the MTH is an SD70M.
K-Line did make a correct SD70MAC many years ago, but Lionel did not use this die for their latest run of SD70MACs.
C32-8/B39-8:
Roadnames include Conrail, Ballast Express, CSX and NS for C32-8, Santa Fe for B39-8.
GE "Super 7" Series:
Roadnames include Monongehela, GE Demonstrator, Conrail, CSX, and various Ohio Central schemes for the 4 Axle version, along with GECX and a few Mexican roadnames for the 6 Axle version.
Feel free to respond with your own want-to-have engines, I want to hear them!