Climactic & Climatic

With a C in the middle – relating to the word "climax." 

Without a C in the middle – relating to the word "climate." 

These two aren't even homophones, but I see them mixed up all the time! Hope this helps.

Rappel & Repel

With an A and two Ps – a method of descending a vertical surface.
With an E – push apart.

Feat & Feet

ea – (n.) An achievement that requires great skill or strength.
ee – (plural n.) Those standy-walky things on the ends of your legs. Or units of measure equivalent to twelve inches.

"Pique" amendment

A couple weeks ago I made the egregious error of omitting "pique" from Peak & Peek. Consider this little striptease my apology. I hope it piques your interest... in grammar!

Peak & Peek

If I could take a peek at the peak of my career, I wonder if I would be looking into the past or the future...

Update: Please accept my humble apologies for forgetting to include "pique." Let's fix that mistake right here.