Brains and also little synapses.  I like the brain earrings, but I wish I could get post earrings without the brain stem.  I know it’s important and helps you breathe and stuff, but it’s not very aesthetic.

A DNA pendant (see p.2, they won’t let me link directly) sure would be pretty, though.  Nice aesthetic design on the part of all those genes.

I also like the rainbow squooshy brain (in bestsellers).