The following is, strictly speaking, not a mnemonic (as or a fortuitous
mispelling had it here earlier, a "pneumonic") but I've always found it useful
to split the alphabet up into groups of four letters:
Alpha-Beta-Gamma-Delta (Almost exactly like English)
Epsilon-Zeta-Eta-Theta (Completely unlike English, but fun to say)
Iota-Kappa-Lambda-Mu (Again, almost like English, omitting the
weird letter "J")
Nu-Xi-Omicron-Pi (Almost like English, the anomaly made easier
to remember by the Xi/Pi rhyme.)
Rho-Sigma-Tau-Upsilon (Exactly like english)
Phi-Chi-Psi-Omega! (Again, fun to say, building up to the final
Omega, which, presumably, everyone knows. ;-)