Given the eclectic nature of this group, I bet there are some great or unusual mnemnonics that people have learned or developed.
Linnean classification:
Karen, please come over for great sex.
kingdom, phylum, class, order, family, genus, species.
Moh’s scale
Toronto girls can flirt and other quirky things Canadians do.
talc, gypsum, calcite, flourite, apatite, (orthoclase) feldspar, quartz, topaz, corundum, diamond.
Any others out there?
Oh, oh, oh, to touch and feel a girl’s vagina - ah, heaven!
Which is, I think, a mnemonic for the twelve cranial nerves. But as IANAD, I don’t know the terms that each word actually stands for. (I picked the phrase up from some novel or other and it seems to have stuck. I wonder why? 
In key signatures:
Order of sharps: F C G D A E B
Fat Charlie Gets Donuts After Eating Breakfast
Order of flats: B E A D G C F
Breakfast Eating After Donuts Gets Charlie Fat
Kudos to the Doper who gave us the new mnemonic for the planets after Pluto got demoted:
My Very Excellent Mother Sent Us Nothing.
I learned:
Fat Cats Go Down Alleys Eating Birds
And here’s one that will be useful to no one on this board:
"Mr. N.L. Man-Q"
My driving instructor taught it to me when I was a teenager: it’s the order of the main north-south streets in Kansas City. (Mission, Roe, Nall, Lamar, Metcalf, Antioch, Nieman, Quivera, in case you’re wondering.) It was eminently useful in my often-confused youth.
I heard this attributed to Billy Bragg, for remembering the notes of the strings of a guitar in standard tuning (starting with the sixth, or top, string):
Every Armpit Does Get Body odor Eventually
Bones of the Hand:
Some Lovers Try Posititions That They Can’t Handle
Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate
A rather boring one for musical modes: I Don’t Play Like My Aunt Lucy (Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, Locrian). I’m sure somebody can come up with a racy one.
freckafree
Did Jupiter get demoted too?
From my programming class decades ago, the order of the 4 divisions of a COBOL program are:
Identification, Environment, Data and Procedure
My mnemonic for that was:
I Eat Debbie’s (do I really have to type the fourth word?)
If I must say so myself, I think I’ll remember that right to the grave - and maybe sometime after that. 
I used to have a rough time with “port” and “starboard” until a friend told me to remember that port wine is red, and port is indicated by a red light. The word “port” contains five letters, as does the word “left.”
My bad! :smack:
My Very Excellent Mother JUST Sent Us Nothing.
They do?
More of a WTF, but back when I was studying electronics we had a mnemonic to remember the colored bands around resistors:
Bad boys rape our young grils but Violet gives willingly, better get some now.
Black, Brown red orange yellow breen blue violet white, (I forget what those last four were but they were rarely used anyway).
Then of course there’s the order of operations in math:
Please pardon my dear Aunt Sally
Powers parenthesis multiplication addition subtraction
Isn’t it “Please Excuse My Dear Aunt Sally”–Parentheses, exponents, multiplication, division, addition, subtraction?
What am I, a math wizard? 
I always liked this one better:
On old Olympus’s towering top, a Finn and German vend some hops
Olfactory, optic, oculormotor, trochlear, trigeminal, abducens, facial, auditory-vestibular, glossopharyngeal, vagus, spinal-accessory, hypoglossal,
Oops. :smack:
OK, let’s try again. The word “port” contains four letters, as does the word “left.”
(Note to self: do not post after drinking too much port.)
That one’s just fine - especially as it points up the attitude that non-modal harmony is a little stodgy and conservative.
“Lassie is not a vegan.”
Lasionycteris noctivagans
Common: Silver-haired bat
I still remember it long after my last Mammology final, which was sometime back in 1997.
SMTP
Send Mail To People
(reminds you that SMTP is outbound mail)