Silver lever with Black clamp.
Initially marketed primarily for cyclocross, these are also an excellent choice for the touring or long distance cyclist, permitting you to brake from the top part of the handlebar. Unlike the 1970s extension levers, these don't interfere with the main brake levers. They install in the middle of the cable run.
24mm clamp for standard road bars.
These can also be used as primary levers without the normal drop bar levers.