Some crafty nerd love for an awesome TA that I had in an organic chemistry lab.
They're little test tubes with a letter floating at the bottom of some suspiciously psychedelic looking liquid.
I just cut out the bottom portions of the test tubes and pasted a colorful bit of paper on the backside to show through. I cut the card so that the letters were attached to the card itself, but I think they could be easily glued if so inclined.
I think I'll be using the same idea for a birthday card very soon...