Brakes.  Pretty important part of any bike we think you will agree.  Here you can replace or upgrade you disc brake system, switch from cable operated to hydraulic, get yourself a new pair of V brake cantilevers, or switch to a more powerful, ligher set of road callipers.  

For example, one of our staff recently fitted a set of Shimano 105 callipers to their winter road bike in place of the non branded pair that were fitted, the improvement was very noticeable and gave much more confidence on descents. 

V Brakes - MTB, Hybrid