I am also always cold.
I would take Maya's first suggestion to heart. Not to sound like a preachy environmentalist, but air conditioning is one of the greatest emitters of carbon dioxide. Raising the temperature a bit will save your skin and the environment!
I, like Maya, always have a pashmina scarf. You can wear it as a scarf or use it as a light shawl. You wouldn't believe how much warmer you will feel with a light scarf around your neck or shoulders.
Layers are the most important. I always have a cardigan with me in the summers, and in the winters a cami or long sleeve undershirt can really warm you up.