I got an early birthday present of a Canon EF-S 24mm f/2.8 STM "pancake" lens. A co-worker had gotten one a few years back and I've admired it since. It's small, lightweight and has a low profile, making it easy to carry around.
A Ken Rockwell review of this lens gives it good marks. He summarizes that
The optics of this lens are superb, and its size make it a complete winner. For $150, you can't go wrong.He's right.