In reply to GridNorth:
Yes wrist warmers make an incredible difference as you will find out.
In general its all about never letting them get too cold - rack up and put crampons on in your walk-in gloves (cheapo fleece ones are often fine), top rope first if possible in mitts to warm the hands up, shake out lots even if not pumped to keep the blood flowing, and if they are getting cold warm them up by your chest if possible (has to be skin touching skin).
Also.. if you keep your body cool to prevent sweating your hands will be colder; getting a bit too hot can be fine when cragging and will keep warm blood going to the hands. Try wearing an extra layer!
Obviously don't follow all of this if you're way away from civilisation as it has the potential to get the core wet and cold, which can of course be dangerous, but I find down to about -20C I don't get hot aches and I'm a skinny guy!
Alan
http://www.fjellogpadleskole.no/