Lights

If you're lucky enough to have a 55 gallon or close-sized tank, good lighting can be quite cheap. Our local hardware store sells Liteway shop-lite fixtures which hold two 4-foot fluorescent bulbs for $8.99. I use two of these fixtures (holding four 40 watt bulbs total) over my 55 gallon tank, with Phillips F40D bulbs ($3.99 each locally) in them. (Many people say that they can't fit two fixtures over a 55 gallon "show" tank, but the brand Liteway is only 4-1/2" wide and a pair fit nicely just laying on the cover glass. Other brands I have seen are unfortunately wider.) This setup satisfies three important factors for aquarium lighting:

1. Uniform lighting over the entire top of the tank so that there are no dark corners or walls in the tank. Dark areas may be aesthetically pleasing to you, but I think healthy plants are more aesthetically pleasing.
2. Full spectrum lights. This means they match the spectral output of sunlight closely, which the F40D does. The correct spectrum is obviously important for photosynthesis, as plants have evolved to work best with the sun's spectrum. "Cool White" and other cheap $0.99 bulbs won't work as well or look as good as a light source since they differ considerably from sunlight, but they can grow undemanding plants if you're broke. Also, don't buy the EXTREMELY overpriced bulbs sold by aquarium specialist companies (up to $30). And don't be fooled by the fact that "daylight" bulbs don't look as bright as "cool-white" bulbs, since cool-whites put out the highest intensity in the frequencies where your eyes are more sensitive, which are not the most useful frequncies for photosynthesis. Any "daylight" or "full-spectrum" bulb will do.
3. Proper intensity. Most people agree that four 40 watt bulbs in a 55 gallon tank is enough light. Really, as long as you have no algae problems and the tank is not overheating, you can't have too much light intensity. Practically speaking, it may be too much (I have experienced "green-water" algae in the past with 2 daylight bulbs and two cool-whites over my 55 gal, which some people say is a clear sign of too much light) so I have adjusted the intensity down a little in the past by putting strips of toilet paper between the lights and the glass cover when algae have gotten bad. This is better than just using 2 lights with no light blockage, as you don't sacrifice item (1). However, algae are often a sign of other problems which are correctable (see algae section). In the end I have always removed the tissue blocking the light after the algae is cured, to provide the plants with as much light as possible.

If you have a small or odd sized tank, the hood that came with the tank will satisfy neither (1) nor (3) above. That's ok, just buy plants that do not require a lot of light. As a general rule, dark green plants are ok with low light levels, and light green or red plants need high light. If you can afford it, add a second light fixture to the aquarium so that there are two light strips above. You will notice a marked improvement in growth. I have modified some fixtures to fit three 15 watt bulbs over my ten gallon tank, although the plants could get by with two. The intensity of flourescent bulbs goes down dramatically in the first 6 months of use, so having a lot of wattage means that you don't have to worry about replacing the bulbs every 6 months.