Square D QOB120 Circuit Breaker 1 Pole 120/240V Bolt-on 20A Breaker (QTY 10)
A nice touch is the Square D brand, and you will find that it helps keep the panel looking tidy.
Square D QO2020C 2-20 Amp Single-Pole Tandem Circuit Breaker
The breaker features Qwik-Open and a Visi-Trip indicator to easily identify a tripped breaker.