Buy ALL OF THE LIGHTS.
A bit (but not much) in constradiction to the others: Dont be a christmas tree ;) That could mean that people dont know what you are and misjudge your distance - which is the most important point.
But I wrote this as a german, we dont have lots of blinking lights for example. They just got legal to mount. So cars are not used to lots of blinking.
Definitely get a good lamp in front and back. Have a bike dynamo lighting on your bike. You can use the battery ones, but if you forget to change batteries or something else happens - your dynamo will always work, its powered by your legs. It's a very useful backup.
Also use reflective elements front, back and most important sides. We call it cat's eyes for obvious reasons. (I mean this
http://www.amazon.com/Bicycle-Spoke-Reflector-Set-Reflective/dp/B00JJ8LPQW/ref=cm_cr_pr_product_top ) Put 4 of them in each wheel.
The most important point in these reflectors is that they
always work and adjust to your "enemy". If a truck has large lights, you light up more, too.
You definitely want reflective clothing. Best is on both legs and both arms, torso and if possible head. The human brain is astounding - people can recognize you are a human just from these 5 points (rings), especially if you are moving. If you ride a bike, you are a very very unique picture with these 5 points. It also means that people can judge your distance fairly good. (Same applies to the cats eyes)