I've tried it all over the years. Neoprene doesn't work.... Rubber gloves get clammy really fast....Ski gloves get wet....

The nicest solution I've found to riding in the 40s and rain is to wear a PVC jacket (one of the cheapies from Performance) and wearing fleece gloves. But here's the trick. Before you put on the jacket, put a sealed (definitely no holes) plastic bag over your gloved hand, wrapping it a bit so the bag isn't all huge of course. Used Walmart bags are great for this. Then slide your 'bagged' hand through the sleeve hole. When you open up your hand, it'll make a nice air pocket inside the bag, like a little microclimate, for your hands.

The elastic in the sleeve hole then holds the plastic bag in place through the harshest conditions for as long as you need (I've done 100-mile training rides like this). No water's getting in there. Your hands will be warm and dry. And they won't get clammy at all.

Definitely doesn't get style points, but it works like a charm!