Bicycle arm warmers are nice. When you get too warm, you just quickly roll them down to your wrists. Pretty flexible, easy to stuff in a pocket, and they do keep your hands warmer.
I put a shell mitt over whatever gloves I'm wearing when it gets colder. That seems to give me another 5 to 10 degrees of warmth.
Hind makes super thin liner gloves that will dry quickly and fit inside most other heavier gloves. In wetter conditions, it's better to have uninsulated shell gloves and thinner layers underneath so each layer can be dried out by body heat at night. In colder conditions, you can get away insulated gloves without worrying about getting them soaked. Any cheap, warm glove will do, as long as it isn't too tight. People often get cold hands from restricted circulation when they try to pack too many layers in a shell glove or mitt. In any case, sleep with your gloves, at least the inner, thinner layers, to dry them out every night.