I just get out my PDA and click on calendar.

Two of my favorite mnemonics are:

"Richard of York gave battle in vain"
= Red, Orange, Yellow, Green, Blue, Indigo, Violet - colours of the spectrum/rainbow)

and

"Here lies beery Bill caught napping on Friday"
= Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine - the next 8 elements in the periodic table after Hydrogen except that I can never remember which day he's caught on.

I'm sure most musicians have learnt "Every good boy deserves favour" for the notes on the lines of the treble clef.