I second the suggestions above. Both the icebike site and the Peter White site have lots of good info on tires.

Here's what my personal experience says: Studded tires definitely help on slick icy surfaces and to an extent just knowing you have 240 metal studs working for you can boost confidence in icky conditions. The big treads help in snow. Nothing helps in (a) slicked-down slippery snow that cars have driven on; or (b) frozen bumpy snow.

I've had great success with the Nokian Hakkapeliitta W240 tires. They're heavy as all get-out, but with all those studs, you don't slip on ice at all. The big treads work pretty well in snow, too.