Temps vary as to rider's circulation and tolerance for cold. For myself, in 25-55 F. temps I like the Gore Windstopper gloves. They do, well--stop the wind. I like them so much I have two weights, a lighter set for the top of this range and slightly heavier, more insulated set for the lower part of this range. But even the heavier set is not that well insulated and for colder temps I go with some lobster gloves (thumb and index fingers like a glove, rest light a mitten) and then to full mittens.

I ride mostly urban, so I don't really always get all my body heat going like a more performance-oriented rider without stop lights would, but when I do ride with more sustained effort, the Gore gloves don't seem to get a clammy as some others I've tried.

You can also go two layers. A wool or poly glove under a thicker "shell" glove.