It’s all good.
I’ve always liked Rotifers.
Saccharomyces cerevisiae, lactobacillus acidophilus, and penicillium roqueforti have all been good to me.
I’m fond of gonorrhea. It’s a Gram-negative diplococci. I made a pin for my Microbiology professor from two bright pink pompons to which I glued googly eyes. I set it in a small box of shredded white paper (the exudate!) and gave it to her after my final in her class. She loved it and wore it to class the next semester, telling her next class that a student had given her the clap the previous semester. Dr. Young was a total hoot.
Yeast. Beer, wine, and fresh baked bread should be reason enough.
Yeast.
That’s awesome! I may have to steal it. 
I just made the flu virus my wallpaper :~
Or head straight to their home page for the full selection!
I like Staph. aureus, the workhorse of the bacterial world. What do you need? I can do that! Just hang on for a couple of generations…
Happy little Giardia are probably my favorites, but I’ll throw out brain-eating Naegleria fowleri just on the basis of being the cause of one of my all time favorite diseases, Primary Amoebic Meningoencephalitis.
I’m sticking with the tried and true Yersinia pestis, carrier of bubonic plague. You’ve got to love a microbe that can gag a flea.
I’m partial to trusty old Ebola a virus that basically turns you to jello
As long as the topic is drifting, I have to make sure everybody’s aware of this site. I have a couple of the neckties.
You could go Agent Smith and use a picture of a stinking mass of humanity.
I’ve always been partial to bacteriophages, myself. I believe they’ve been linked above.
Has anyone linked to the plush microbes yet? (I didn’t read each post, but *did *search for plush and for ThinkGeek)
Post #12. 
I was going to put in a vote for the slime mold, but then KGS had to mention the radiovorous Chernoble fungi, and now I’m torn. Both, of course, are incredibly cool.
Ah, bitten by the curse of the ambiguous link… I did look, I swear - but I wouldn’t have clicked all the links in any case.