Peak, as a noun, means summit; as a verb, it means maximize.
- Those records show Gracie is at the peak of her running career.
- At what age did you peak in your running career?
Peek means to peep or snoop.
- Peek into the window to see if Karol and Jo have left the house.
Pique means to excite or irritate.
- Did you pique his interest with your sales pitch?
- After hearing those comments, Ed is definitely piqued.