I love the Aerostick Elkskin Ropers. I wear the uninsulated ones down to about 40 degrees or so and use my heated grips as needed. I wear the insulated ones below that and they keep me comfy down into the 20's. I can extend that by wearing their triple digit rain gloves over the ropers.
One of the things I like best about the ropers is that the elkskin seems particularly sticky so you don't have to squeeze the throttle as hard (I don't have cruise control) and my hand doesn't get fatigued as much as with other gloves.