Depending how cold we're talking, I'd like to throw hand warmers into the ring.

Circulation to your fingers travels over the back of your hands. When that blood gets chilled, the vessels in your fingers constrict, slowing circulation. Once that happens, it doesn't matter what glove you're wearing, your fingers will be cold.

If you toss a hand warmer in the *back* of your glove or mitt, you can wear a surprisingly light glove.

They go for less than $2/pair, and last about 8 hours. If you toss them in an air tight baggie when you're done with them, and store them in the freezer, they'll stop reacting and be good to go next time you ride.

These get quite hot, so they're not necessarily appropriate in temperatures much above freezing.