For diesel trains, CB&Q's Pioneer Zephyr has been produced by American Flyer, Lionel, MTH Premier & RailKing, and 3rd Rail-Sunset. Mark Twain Zephyr versions have also been produced.
I would love to have a detailed CB&Q streamlined Aeolus Hudson steamer in 3-rail O-gauge. Precision Scale has made an expensive & beautiful version in 2-rail O-Scale. MTH has made versions of the Aeolus #4000 & #4001 with their C&O yellow belly tooling. Although not very accurate, I really like its look.