What is your shifting setup? If you have bar-end shifters, or thumb shifters, then mittens might be the way to go.
Here in Boston, I've been riding exclusively with Outdoor Research PL-400 gloves when its 20 degrees and above. When its below that, I switch over to the PL-400 mittens. Neither offer much in terms of wind-resistance, so if its really frigid, I layer a thin waterproof or wind shell over them. REI sells a novara brand lobster glove that also works really well, but its pretty bike specific and bulky. Personally, I just like to use my backpacking gear for cycling.