You're going to get your best snow and ice performance out of an actual winter tire. Some offroad tires and all season tires are better than others for this, but none will be as good as a winter tire.
Winter tires are often soft and squishy though, and will only last a few winters probably, especially if you're on dry pavement often.
I'm taking the same route others have mentioned, with dedicated tire & rim combo's for dedicated applications. Soft 8's and Bridgestone Blizzak DM-Z3's for november thru march, high quality all season tires with my aluminum renny wheels (don't like to use in salt) for the rest of the year, and finally I've got another set of rims for putting on some off road tires next year for occasional use.
Tire rack compared studless winter tires with studded winter tires and all season tires on ice and the studless winter tires were clearly the better choice, due to their siping. See this test result:
http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=94
See this for siping info:
http://www.discounttire.com/dtcs/tireSiping.dos
Finally, Check out the Blizzak DM-Z3's, they are on sale for about $80 each because they have a new model out that replaces them, the DM-V1, which looks basically the same. Here is the DM-Z3 on closeout. TONS of great reviews. This site isn't full of cherry reviews on all tires either.
http://www.tirerack.com/tires/tires...R6BZDMZ3&vehicleSearch=false&fromCompare1=yes
Here are some pics of DM-Z3's I bought and am waiting to put on. Check out the siping in the last 2 pictures. Basically just tons of tiny cuts.
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