I think everybody knows that one of the greatest dangers of riding a motorcycle in traffic is not being seen by other drivers. Visibility of you and your bike can make you better off where safety is concerned.
One of the easiest and cheapest upgrades you can do is change out the stock light bulbs. Do not get me wrong the stock lights are just fine...for some. But if you want to make a difference in seeing and being seen, then this is the ticket. I changed both the rear brake light bulb and headlight to something a little brighter and it only cost about $45.

I switched out the stock rear brake 1157 bulb for a 2357LL. What's the difference? As far as brightness for normal operation...none. However when braking the 2357 bulb is brighter than the 1157 (42 lumens vs 32). The LL simply means longer life. Cost for two bulbs: about $5.00

I also changed out the two headlight bulbs. I replaced the stock H7 bulbs with Philips Motovision Bulbs. these are designed specifically for motorcycles. They have a unique orange reflection that helps you see and be seen (headlight appears "orange" but light output is bright white), they put out about 40% more light than standard halogens and a longer beam of light.
Cost per bulb: about $20.00

So if you are looking for an easy, inexpensive light upgrade this is a place to start. Note the keyword 'inexpensive'. You may be able to find other H7 headlight bulbs that are brighter compared to stock but maybe more expensive or lower quality.

Philips is known for making very good lighting products. Some others are listed below.
PHILIPS MotoVision Light Bulb (pic is bulbs installed on my bike)
PHILIPS Xtreme Power H7
Philips Blue Vision
Bikemaster Vision X H7 Bulb
GE Nighthawk H7-55NH/BP
Sylvania SilverStar Headlight Bulb