I like to make my own studded tires with #6x1/2" self-tapping sheet metal screws in cheap knobbies.
Total cost around $25 for two. $14 for a new pair of knobbies, $5 for screws, some taxes and old inner tubes from donations to the shop. I make one for my front and give the other to someone else for their front tire.
If you decide to go this route, check the screw size versus the lugs you want to stick them into, because you really only need a little bit of a point sticking out, and you don't want to split the lug in half with a fastener too large for it.
In my experience, they work really well on road ice and that hard ice-snow combo you get on city streets.
Directions are here:
http://www.icebike.org/Equipment/tires.htm