Head Set Bearing Protection
Inner Tube Head Stem Seals (upper and lower)
Rain and dirt can ingress into those head set bearings, even if you are using sealed bearings. Over time bearings can rust and breakdown with potentially costly and sometimes disasterous results.
One solution is to fit a neoprene seal around the headset, but they are often not a good tight fit and of course its just more of your hard earned cash that you are shelling out.
Instead, when you next service your bearings, just cut off a length of old inner tube about 80mm long and stretch it over the head set bearings. Make sure that the tube seals against the frame for a few millimeters, enough to make a seal but not to impart significant drag as you turn the handlebars.
You can also do the same for your seat post to stop water running down inside the frame and causing problems with the bottom bracket.
Voila, a simple and cheap solution!