If you ride 'cross, or if you commute on a bike with traditional drop bars, and you don't already have a set of top mount brake levers you really need to get a pair. Really. We're not usually this dogmatic, and the truth is you'll survive without them, but wow is it nice to have them.
Put simply, top mount levers, such as the ones pictured here, provide a second position for you to brake from, so if your hands are on the tops of your bars you can brake without changing position, which in some situations means maintaining crucial control of your bike.
Your bike's brake cables pass from your traditional drop bar brake levers through these secondary levers and on to the brakes themselves. Either set of brake levers can be pulled to activate your brakes with equal force. They really are a great little invention.
We have a few sets in stock right now, and they only cost $30 for the set, but if you come in to buy a pair be sure to purchase ones that accommodate the correct handlebar diameter - we have both standard sizes in stock.