I use the Kisan Tech T50W TailBlazer brake light flasher. It's saved me a couple times. The closer the car is, the more likely you *need* the flasher to grab the driver's attention. It flashes fast enough that there's no ambiguity about whether the brakes are being applied.
It also happens to help that all the cop bikes around here have the flashers on their brake lights... so when drivers see that, they make the assumption that you're one of them, and suddenly start driving very conservatively.
I can also attest that the Kisan Tech T50W TailBlazer works with LED lights... at least the one I installed: CREE LED Q9 1157 Red
It's the same LED brake / tail light mentioned here by az_slynch:
http://www.kymcoforum.com/index.php?topic=11926.0It's ungodly bright, and really gets people's attention when it flashes.