I'm sure everybody knows the rule of thumb for spelling I before E, except after C or when sounding like A, such as Neighbor or Weigh. Though that last bit is often left off. Which is weird.
Another mnemonic is to look for a rat in the word separate.
What other ones have you heard?
One I haven't heard in a while, and I don't know how effective it is, but people scream eeee eeee eeee when passing a cemetery.