I just installed an intelligent third brake light flasher on my 4Runner. The IBF4 model flashes the CHMSL (Center High Mounted Stop Lamp) 4-5 times the first time brakes are depressed then goes solid red. The number of subsequent flashes reduces depending on the amount of time between each brake pedal depression.

This is a great way to grab the attention of the inattentive person behind you, yet doesn't annoy them w/ a strobe effect. Works great and was an easy three wire hookup, tho it does require you to cut the green wire leading to the brake lamp. It's sealed in epoxy and you just stuff it inside opening before replacing the lamp housing. They're usually found on ebay for about $20, but you can see details and order direct here:

http://www.comagination.com/bflasher.htm

This along w/ the rear fog mod gives following drivers absolutely NO EXCUSE... you can't miss all those red lights in the rear, esp. if one of them is flashing.