Another Wacky Word pair that trips people up is that of breathe and breath. (The latest sign I saw of this had to do with helping people to "breath clean air"!)
This pair is tricky, along with all of the ea pairs, because ea says short e and long e--all by itself. For example:
1. Today I will read the book.
2. The leaf fell to the ground.
3. The thief is going to steal the diamond.
The key to knowing whether to use breath or breathe is to consider the pairs that do have e at the end--it is there to show that, that word is the long e one (not the short e one).
1. Take a deep breath (breth--short e).
2. Breathe deeply (long e).
3. He took great pleasure in it (short e--plezz).
4. They want to please him (long e).
While there isn't a fullproof trick (like their/there and affect/effect), it does help to keep in mind that if one of the set has an e at the end of it, it is there for a reason--in these cases, to make the first vowel say its long sound--breathe (long e) vs. breath (short e).