What can you grow with a standard commercial hood?

The short answer is no, not really. 1/2 a watt per gallon is low for low light. Maybe a Java fern or anubias, but its really not enough.

If you're inerested in going planted try AHSupply.com, give them a call even. Very helpful folks. You may be able to retrofit a 2x36w or even the 96w kit into your existing strip for about $100 (kit and bulbs).

i have 1 watt a gallon in a 20 long, and i have anacharis and recently put in java moss. i float the anacharis and i tied the java moss to drift wood. the anacharis grows pretty fast, i can imagine it being ok in your tank, although im no where near an expert.

I have a single 38W tube in a 60Gal tank. I grow all sorts of plants without too much problem.

Go for plants specified as low light and make sure to satisfy their other needs, ie water conditions, fertilisation and preferably co2 (diy sugar/yeast is quite easy)

I have a successful amazon sword that's now 20 inches high, my onion plant grows well, I have to keep pulling up spiral Val as it spreads all over and my java ferns keep reproducing.

Under my origional light in my 25g long, 20 watt tube, I was able to grow Amazon sword quite nicely, with no co2. My tank was overstocked so, I think I had enough co2 and fish waste. Also, anubias did ok. And, you'll not go wrong with hygrophilia polysperma. Indestructible plant. Nice green color, turns red towards the top of the water, and it can grow floating too.
Anacharis did ok for me if I let it float, but it got straggly and so I pulled it out. You can try another bulb as well, like triton (worth the price) or tropic sun. The bulbs designated as 'floral' are expensive and you can get the same results using 'daylight' or high output flourescent.

With the exact setup as you, same tank and lighting, I was able to grow anubias, vallisneria, limnophila sessiflora, java moss, and crypts. You should also be able to grow java fern.

You mentioned wanting to increase light. What I did was retrofit a 55 watt power compact light into my fixture. This gave me a lot more light, the only downside is it's still only 2', meaning there are dark ends on the tank.

You should be able to keep a number of plants alive. However, they won't grow much and only very slowly.

edit: except for hornwort. I forgot to mention it. It will grow like crazy in any lighting basically.

I've got a 15-watt wide-spectrum tube in my 15-gal tank, and my plants are doing fine. So far, I've had good success with java fern (both the "normal" and the "windeløv" varieties), java moss, Echinodorus quadricostatus (which is nearly growing out of the tank at this point), Hygrophila corymbosa, and Vallisneria spiralis (which is threatening to take over and completely shades everything if I don't keep it trimmed). My Echinodorus tenellus is slightly less successful-- it grows very slowly, but has recently started putting out runners. Bacopa caroliniana did okay, though I had trouble with staghorn algae growing on it, and it lost some of its lower leaves due to the poor lighting.

The hood is just a cheap plastic one with the fluorescent tube mounted on one side (hey, it was free, and beggars can't be choosers...), which means that the lighting is very uneven. The java moss, java fern, and hygro all do fine on the opposite side of the tank, but the two Echinodorus plantings did poorly until I moved them to directly under the light. Believe it or not, it made a huge difference and now they're sprouting all over the place. I use root tabs for them, as well, and that seems to help.