i remember asking this last winter season for my road bike which only accepted up to 700x28, i was disappointed to find out winter tires weren't made on the thin side. i have a new bike, the crosscheck and it accepts up to 45 i think. we got 40 at the end of last season (Nokians) so we're excited to use them this winter.

last year i asked a friend who rides winters in Denver regularly and he said what he does is just get a beater bike with clearance for wide tires and use that as his winter bike. he just went back and forth between the bikes in the winter months depending on what was on the ground or forecast to hit the ground that day.

best of luck your search!

45nrth Xerces, 30c is the smallest I've seen:
45NRTH | Unparalleled Cold Weather Performance

Continental 4 seasons if there's no ice and snow. If there are, you need a bike with more tyre (and mudguard) clearance.

I bought a 700Cx28 Vittoria Zaffiro III from Nashbar for my road bike.
It is a very grippy tire, has puncture protection and is a decent weight.
If I were still commuting on that bike in the winter, these would be my first choice.