First rule: don't ride at night...
... But if you must ride at night, get a tail light! Everybody should have a tail light. Whether you commute to work, ride at night, ride during the day, ride two times a year... get a tail light, and make sure it is a good one. If you opt for the cheap, affordable route, you are not going to do yourself any favors. I did the research, and this is the best tail light for the money. It is loaded with features, and works just as it should.
Most importantly, it is extremely visible, even during the day (I attempted to photograph this feature, but it overwhelms the camera!). During group rides, I have received complaints from the people riding behind me that it is "too bright!" It has numerous flash settings, along with two yellow LED's for side visibility. It is easy to install and remove, so you don't have to worry about sticky fingers at the lock-up. It has a slender profile and sharp looks. It has a built in reflector, to satisfy the legal requirements. Finally, as an added benefit, it is fairly light weight. Ultimately, it has everything you need and nothing you don't. It is the best out there.
Don't cut corners with your safety equipment. Too many cyclists are injured or killed on the roads. Most of these tragedies can be avoided with a little common sense and some high visibility gear. Extend your riding career, invest in a quality tail light.
This light has probably saved my life... more than once.. but I will never really know for sure.