Most r-comp'ers still run their race tires during cold weather, it just takes a lot longer for them to get warmed up.
If you are in the market for street tires:
Dunlop Direzze Z1 Star Specs ( I run these and love them! )
Bridgestone RE-01R or the new RE11's ( or some RE number )
Those are a good place to look to get started anyway. Lots of good info on each of these in this section.