So, how many flashlights do you need? At least two more.
Since it is dark about half the time—and almost always when trouble lurks—I strongly recommend having flashlights everywhere. Start your collection by getting at least one quality light from a company like SureFire, then get a few from other manufacturers, too.
In my opinion, six inexpensive flashlights scattered around each car, the nightstand, on your desk, etc., beats the hell out of a $300 astronaut-blinder that's nowhere within reach.
But what features do I look for? Well, the brighter the better—go for at least 120 lumens. A strobe function is a very good feature, and pointy things on the bezel are great if you have to use the light for more than illumination. A lanyard or wrist strap is an option you shouldn't overlook, because it ensures the light will stay within reach if you trip and fall or drop it.
For activation, push-button "momentary on" is my favorite, because I control when and where the light is shone, but "constant on" can also have advantages. I do not like the "dim first, bright second" mode on some models—the light always seems to be dim when I want it bright. More dexterous folks may like that feature, though.
Brand wise, I am partial to SureFire, but I own and like flashlights from other brands, especially Streamlight and Insight.
Here are some suggestions for First Time Buyers:
My top pick is the SureFire G2ZX CombatLight, because it has the rubber ring around the body. The SureFire P2ZX Fury CombatLight would be my next choice cause of the high output of 500 lumens. For those on a budget, the least expensive SureFire model I've used is the G2 Nitrolon. It's a great light for the money. If you are looking for a small, but effective light for pocket carry, the EB1 Backup is a great choice.
There are other good brands out there. Most are less expensive, but as long as it has a push button on the end, at least 100 lumens and you can add a lanyard or a ring later, the light will most likely fulfill your needs. Models powered by AA batteries are also available. These batteries are much cheaper than the lithium versions powering SureFire flashlights and other tactical models, but they won't last as long. Good examples of such lights include the Streamlight Nightfigher X, Scorpion X and ProTac 2L.
One good light is the minimum, but you need to have them all over the place—in your car, pocket, purse, desk, nightstand, etc. Be prepared. Stay Alert. Stay Alive.