Success - Double the c and double the s and you will always have success!
Together - To get together, you have
to get her!

Friend - A friend is a fri
end 'til the
end!
I still use those from time to time. There is also the Right Hand Rule. Helpful determining the direction of the magnetic field created by a moving current (or something). Is it really a mnemonic device if you don't remember the details?
I also am sure you, Wordwind, as a music teacher of youngsters, know all the Every Good Boy Does Fine, FACE, All Cows Eat Grass, etc. mnemonics for learning the notes of the staff.