Here's a set of mnemonics i made after hearing my friend Sean's idea of a mnemonic to remember the major scale whole-step/half-step sequence, his original went thusly:

Why Would Harry Wear White Woolen Hats

Of course then I had to keep it going because of my love for Harry Potter as well as nerds wordy things. Here's some more major mnemonics:

When Would Harry Wave Wands? While at Hogwarts.
or
Why Would Harry Wave Wands While Hammered?
(for the college students)

Minor(Aeolian) scale--WHWWHWW
When Harry Waves Wands His Wrist Whirls

Here are some for the rest of the modal scales...

Locrian--HWWHWWW
Hagrid Will Wash Hippogriffs With Wet Washcloths

Dorian--WHWWWHW
Wormtail Hides While We Watch Horcruxes Whither

Phrygian--HWWWHWW
Hedwig Will Wait While Harry Writes Well

Lydian--WWWHWWH
Weasley's Wizarding Wheezes(the shop) Hawks Witchcraft and Wizardry Humor

Mixolydian--WWHWWHW
the Whomping Willow Hurts! it Wants to Whack Harry and Weasley

Here's even more scales!

Mixo-flat sixth(Hindu Scale)-WWHWHWW
Wince When Howlers Wildly Harangue Worthless Wizards

Melodic Minor Ascending- WHWWWWH
Whimsical Hogsmeade Weekends Will Windup Waning at Honeydukes

Chromatic Scale-HHHHHHHHHHHH
Helga Hufflepuff's Heir Hepzibah Hides Her Heirloom; Hermoine Harms it Heavily inthe "Hallows" Hardcover (with a basilisk fang)

Take that Voldemort!!!