There is no one answer to your question. Where are you riding? Do you want to see or be seen? For how long will you be riding? Where do you live? What tempture range will you be riding in? Will you be riding while it is raining and snowing? All these things effect which light is good for you.
Check out the commuting section of the board for some active threads on lighting.
I'm riding in the upper peninsula of Michigan. I just want it to commute around town so no car hits me while I ride. I will also use it during the school year. It gets pretty cold here so I don't want it to stop working, but I can charge it up every night as needed.
Generally for winter riding, cut rated lenght of light's time by 1/3 or 1/4th. It all depends on how fully charged batteries are and how cold it is during your commute. Always carry a backup light. Small flashlight you can bungee to bars is better than nothing.
I have the Cygolite night rover extra. It has a 10 Watt spotlight and a 6 watt flood. This makes a total of 16 watts when both are on. With 16 watts I have very good illumination in the city where i am aided by street lights.
In the country in total blackness, the illumination is acceptable to ride safely at 15 mph or so, but at higher speeds on roads with potholes etc., the light isn't as good. In those riding conditions you need a light that will really light things up so you don't end up in a pile somewhere.
I am able to get along with mine out in the country on gravel roads on my early morning rides. I usually leave an hour or so before sun up from town, so this really only leaves me with 30 minutes or so of using the light. The sun then comes up and helps me out.
I can safely tell you that the more watts you can get, the better. In your price range you will be just looking at Halogen lamps, so look for the lights with the most wattage. Only a couple watts makes a HUGE difference!
The link to the 2 0watt lights that the other poster gave you looks like a good set of lights. They basically look like the lights made by a guy that has a product called Laser Edge. View them at bicyclelights.com. Look for a water bottle type battery as they seem to have the most on time. Don't worry about looking for a "smart" charger.
You can buy a cheap appliance (christmas tree) timer to turn the charger off at a prescribed time.
I don't recommend the cygolite for you even though i do like mine, however the switches on this light are horrible. Many 10 cent flashlights have the same design for switching off and on. That means they eventually won't work. I have had to take mine apart a couple times to screw with bending the tabs, etc. to get them to make contact. A thumbswitch is a very nice idea and much better quality!