For Christmas, my loving sister gave me E. coli. She also gave me a lovely protozoan parasite, Giardia lamblia. No, not in the potato salad and water. These lovelies were stuffed replicas (1,000,000x the size) of the actual bugs.
If you ever wondered what Streptococcus pyogenes (strep throat, flesh eating bacteria) looked like, wonder no more:
And finally, because I am a twisted EMSer at heart, my belated gift to you: the clap (Neisseria gonorrhoeae)
These are fun, great gifts for the equally twisted healthcare provider on your list and amazing props for teaching. You can see them at: Giant Microbes.