There are lots of photos of unique bikes but I'm wondering if there are any bikes that have significant mods for winter use.

full fenders, studded snow tires (now) and 300lumen headlight for commuting on dark mornings.

There's no need for any special mods to the bike... But full fenders and studded tires will make your winter riding safer and more enjoyable. Singlespeed and fixed gear drivetrain is good for winter ,because it requires no maintenance.

ya, no mods. Just have studded tires which are still hanging on the wall. Actually going to build a second dynohub wheel for the front and have been waiting for the kids to have some time to learn how to build their dynohub wheels. I also got Berthoud fenders to replace the horrible planet bike explodofenders I have been suffering with.

I got tired of wearing through rims and replacing too many parts of a derailleur drivetrain so I bought a nashbar steel commuter and made a "few" modifications.

Dumped the silly flat fenders for full SKS versions. Replaced the rear rack with an axiom journey so it matches the rest of my commuters and makes mounting my backrollers a snap. Switched the slicks for Nokian 106's. Pulled the rear hub apart and added grease to help waterproof it. Pulled the rear wheel apart and greased where the nipples sit on the rim and added anti-sieze to the spoke threads. Pulled the front rim and rebuilt around a SA drum brake (grease between nipple and rim, anti-sieze between spoke and nipple). Dumped the rear brake and added a roller brake (no more rim wear on either wheel). Applied frame saver. Pulled the headset apart and repacked with ample grease. Pulled the seat post and stem to apply grease. Pulled the bottom bracket and applied anti-sieze. pulled pretty much every fastner (peddles, water bottle cages etc) and applied anti-sieze.

Guess I'm at the other end of the spectrum, but I'm fairly happy with it so far and I know things aren't going to corrode together.

I have a second wheelset with studded tires that gets swapped over. Aside from giving the bike a good lube and tuneup, the other thing I do myself is strip off the water bottle cages and racks. A backpack or Camelback works better for me in the winter. Salty slush makes a mess of panniers.

I'm still wondering what sort of things you'd "mod".

I swap my three-season tires for studded snows, swap the three-season fenders for wider ones, and use a cassette with lower gearing since the studs are harder to push.

Maybe I've been doing it wrong for the past seven years.