What mnemonics help solve common linguistic issues?

Example: i before e, except after c.

Are there mnemonic devices to help remember other spelling and grammar issues? Bonus points for pointing out exceptions to the rule.

Another spelling one:

necessary = never eat chips; eat salmon sandwiches and remain young.

To continue with the spelling theme, there is A RAT in 'separate'. This has helped me at times. I wish someone would come up with one for 'definitely'.

I've become rather fond of the expression "an hour and a half"; it's a quick way to remember which of the two articles "a" or "an" should I use in a situation.

Week vs weak. As they say, unity is strength. Hence, two 'e's united can not be lacking in strength.