How nerdy: a coffee cup with the caffeine molecule on it!
Since I'm a pharmacist, I like the chemistry reference, and I've always been partial to glass coffee cups. They're not that easy to find, but they remind me of the glass teacups we owned growing up. I used to feel very grown-up when I'd make myself a cup of tea in a glass mug: not only was I handling boiling water, I was pouring it into glass!
What's your favorite coffee cup? C'mon, I know you have one, we all do!