I've recently been using the Dominic System for creating tone mnemonics, and it seems to be quite helpful.
For those who aren't familiar with it, the Dominic System creates mnemonics from two-digit numbers by associating each digit with a letter and each two-digit number with a person (typically someone with those initials). See
http://www.ludism.org/mentat/DominicSystem
or
http://en.wikipedia.org/wiki/Mnemonic_dominic_system
for more details.
I am using this as follows: each tone is a number 1-5, so to remember the tones in 有期徒刑 yǒuqītúxíng "set term of imprisonment" I have to remember 3122, which is CABB translated into letters. For me, CA is Christina Applegate, while BB is Mr. T (B.A. Baracus), so this becomes the mnemonic "*Christina Applegate pities the fool* as she _sets_ his _term of imprisonment_". (The Dominic System is actually overkill for tones, as you only need the digits 1 through 5, but I'm using it for other things as well.)
Just like using character composition mnemonics, this helps mostly in the initial phase when you're learning a brand-new item. However, it's unfortunately quite personal as the Dominic System requires everyone to invent their own mnemonics for the numbers 0-99, so I can't share these mnemonics.
James