Get a trainer (fluid style, not magnetic or wind).
Get a mountain bike.
Look into studded tires.
Ride on weekends when you can go out at the best time of day.
Commute to and from work by bicycle.

Take a spinning class.
Make an evening of it and lift weights, run on the treadmill, and row as well.
Go swimming.

Cross-country skiing
Snow shoeing
Skating
Long brisk walks in the snow