The Brake Buddy is the best known unit out there, but there are better alternatives, most of which are cheaper. I think by far the best product for the money is the US GEAR Unified Tow Brake Towed Vehicle Kit
US GEAR Unified Tow Brake Towed Vehicle Kit
Ok, that link above goes to the USG on ebay for around $600... mfgr website list the unit much higher, go figure....
You might also want to look at the
Both cost about HALF what the brake buddy cost, both are porportional braking (brake buddy is NOT)... Very much worth looking into!!