DS loves these - he has nerve, bone,e coli, t-4 and others , this year he is getting skin! Stuffies for the science crowd
Giant microbes DeHe
Yersinia Pestis has been on my personal Christmas wishlist for many years.
{sigh}
Going into DD's stocking this year--
awww-- you didn't think that I was really going to spoil the surprise, right? She reads everywhere that I frequent, sadly. Teenagers.
Things which were popular with her in years past:
Dissection kits
Tape
Paper airplane book (with really awesome ideas and a discussion of the design/physics)
Crystal Radio kit
Solar insect/creature kits
Lego Minifigs
Playmobil minis-- especially quirky/ironic stuff. The Hazmat crew still lives on DH's desk at work. ROFL!

Gaming stuff-- minifigs, dice, etc.
Admission to a local exhibit or event
Software