What should I look for in good gloves for raynaud's syndrome?

Dexterity, warmth. Gloves should be warmly insulated, and have a breathable, waterproof coating or layer such as goretex (wet gloves get cold). They should be easy to get on an off, and not be too tight (tight-fitting gloves can decrease blood flow). Gloves should allow good dexterity, so the wearer doesn't have to take them off outdoors (be able to use keys, zip up jackets, etc..., without taking gloves off).
Warmth. Mittens may be better good palms to, hold things. Try them in the freezer!