Inspired by KeithS's question about ATPLs and category/class ratings, I figured I'd throw another type-rating/airline-operations puzzler at you: are there any aircraft currently in scheduled airline service (i.e. operated under part 121) which would not require a type rating to fly? (I know part 135 operators often fly small aircraft due to the nature of their operation, with more intermittent or even on-demand service and the smaller locales they fly into.)
Cape air has a fleet of 83 Cessna 402s, some of which are involved in its Part 121 operation.
Regional airlines in Hawaii and Alaska also operate the 208, but they seem to be part 135 operations.
Cape Air seems to be a Part 121 carrier, and since they fly the Cessna 402, that might be an answer.