When we think of tracers, more often than not we think of military applications and belt-fed machine guns, with the tracer rounds being used to help direct lines of fire.
In defensive situations, this rarely enters into the equation, of course, but we sometimes like to let our hair down (metaphysically, at least; some editors have a harder time than others accomplishing this...) and have fun. When safe to do so, letting loose with tracer rounds at dusk (or at night, assuming of course the range permits and it is safe to do so) is, at least, an interesting study in ballistics.
PolyCase Ammunition announces the "Firefly" line of the company's Inceptor ammunition that includes a 9 mm tracer round. The bullets are 81-grain round-nose projectiles made of the company's proprietary copper/polymer blend and contain a bright tracer compound.
MSRP: $39.99 for a box of 25 rounds.