My grandmother taught me one to remember how to spell “geography”: “George Earl’s Oldest Girl Rode A Pig Home Yesterday”. Still makes me smile.
There’s “a rat” in “separate”.
A few of us artsies had to learn some neuroanatomy for our psychology class. We were having some trouble differentiating between the cerebellum and the basal ganglia. For our purposes all we needed to remember was that the cerebellum is for rapid movements (I remember birds have big ones) and the basal ganglia is for slow, deliberate ones.
So my friend said “Cerebellum” really fast (try it! it’s fun) and “Baaaassssllooooooow ganglia.”
Now I will never, ever forget.
I learned it as, “Mary’s Violet Eyes Made John Stay Up Nights Playing.”
I still have to recite 'Thirty days hath September, April June and November", and work it out by elimination.
And yes, these are mnemonics, they’ve not restricted to acrostic rhymes. Anything which assists the memorising of a specific piece of knowledge is a mnemonic.
In navigation, for uncorrecting (going from a true course to a compass or magnetic course):
True Virgins Make Dull Companions At Weddings
True (course)
Variation
Magnetic
Deviation
Compass
Add
West
So, 145T + 2W (var) = 147M - 1E (dev) = 146C
When correcting:
Can Dead Men Vote Twice At Elections
Compass
Deviation
Magnetic
Variation
True
Add
East
My Catholic-school-educated aunts learned the mnemonic “Will yoU Come For Kitchen Pans Friday?” for the Seven Gifts of the Holy Ghost (Wisdom, Understanding, Counsel, Fortitude, Knowledge, Piety, Fear of the Lord).
In a magazine article about Scrabble, one player was quoted as saying “KA takes BETSY” (the word KA, a term from Egyptian mythology, can be extended into five acceptable three-letter words, namely KAB, KAE, KAT, KAS, and KAY).
From electronics school:
Eli the ice man.
E (voltage) leads current (i) in an inductor (l)
current (i) leads voltage(e) in a capacitor ©
Which reminds me of one for wiring multiple batteries together: Save Pay (SAV PAA)
Series adds volts;
Parallel adds amps
I pinched my aunt Thelma. That’s a mnemonic for… um… something biological. Eventually, lo and behold, it came dribbling back to me: interphase, prophase, metaphase, anaphase, telophase - the stages of mitosis.
I had a different one for kingdom, phylum, etc. Kings pick cherries off fine green saplings.
You can sort of tell my high school biology teachers were middle-aged women, can’t you?
soh cah toa
A pretty common mnemonic for trigonometry, but to make it a little more interesting, a classmate extended it to “sailors often have certain anal happiness to oppose anger”. The odd time I need to use trig I remember the first, but the second always seems to pop into my mind a minute later!
I had a couple from my first biochemistry course that I made up (and don’t make that much sense) which have come in handy about amino acids:
“History likes Argentina because it’s basically positive” (Histidine, Lysine and Arginine are basic molecules and positively charged)
“I ate acid and it was a negative experience” (Glutamate and aspargate are negatively charged acids)
I had one from grade 7 or 8 science which was abbreviated as TACO but I don’t remember what it could be.
Of course, mnemonics aren’t limited to phrases based on initial letters. My all-time fave, which I use A LOT, is “Right tighty, lefty loosey.”
There was a thread during the demotion of Pluto brouhaha about how “My very excellent mother served us nine pizzas” should be altered.
The hands-down winner, IMHO, was “My very economical mother served us nothing.”
I learned the same, appended with “Get some now”, for Gold, Silver, and no band, relating to percentage of resistor tolerance.
Jupiter got demoted as well? 
(I assume you meant to type “My very economical mother just served us nothing.”)
mnemosyne: I can’t help you with the TACO mystery, but your mention of it reminded me of my seventh-grade science teacher’s use of the terms CHO and CHON to signify the Carbon-Hydrogen-Oxygen composition of carbohydrates and the addition of Nitrogen to form proteins.
In my astronomy lecture at Michigan in 1987, we had a contest about this.
My entry (which lost out to something much less clever):
Out Back Australians Favor Grilled Kangaroo Meat.
May I have a large container of coffee?
My favorite, from back in high school:
Kinky Percussionists Come Over For Great Sex
Yeah, I hung out with a lot of band nerds.
Then you’ll remember the order of sharps and flats mnemonic – the only one I know that works BOTH forward and backward:
# Fat Charlie Gets Donuts After Eating Breakfast
b Breakfast Eating After Donuts Gets Charlie Fat
I learned it as Kings Play Chess On Fuzzy Green Squares.
As seen in a recent Sky and Telescope magazine editorial:
Many Very Egotistical Malcontents Just Screwed Up Nomenclature
Resistor color coding:
Bad Boys Ravish Only Young Girls But Violet Gives Willingly.
Black Brown Red Orange Yellow Green Blue Violet Gray White
Roy G. Biv is Mr. Rainbow.
Red, Orange, Yellow, Green, Blue, Indigo & Violet.
From math: How I wish I could recollect pi easily today.
The number of letters of each word gives us 3.14159265
The planetary Mnemonic, I never used, I just memorized the order very young. The Mnemonic needs to be altered now that Pluto has finally been demoted.
Jim