Is there a good way to go half way with plants???

It's easy to keep plants, you just have to know which ones... ex: Anacharis, and Cabomba are both fairly easy to keep.

Flourite helps a lot, and if you could change out those 20w, for some "Floraglo" lights... They are very nice for keeping plants. Oh, and if you're scared of an overpopulation of snails, be sure to wash your plants, and look them over carefully before adding them to the tank.

plants can be very cheap. the best decor for the dollar is plants on driftwood. java fern, anubias, java moss. these will "live" with your current lighting. but most plants that are above the low light level require you to spend at least 100 bucks

imo, skip the flourite. its too expensive to fill a 120 for a few plants. plus the 3 kinds of plants i listed dont need rich gravel or high light.

Lighting will be the biggest thing. Two 20 watt bulbs on a 120 gallon tank is not just inadequate, its absolutely ridiculous. You couldn't possibly grow any plants, I dont even see how that is enough light for illumination too see your fish properly. I can not imagine why any tank manufacturer would supply such grossly inadequate light on a tank that size.

Ideally you should have 240 watts of light at the very least to grow plants. If you have a wood canopy or hood, you can easily retrofit enough light using power compact fluorescents for around $250 from AH supply or some other retrofit company. If you do not feel comfortable wiring your own lights. your only alternative is to buy fixtures, either something that will sit on the tank, or hang above it. Here you are looking at 300 to 500 dollars.

If you want to get real cheap and a little tacky looking, you can buy 48" shop light fixtures that hold two 40 watt tubes. You would need a glass cover on the tank, and then you would need to cram as many of these on top of the tank as will fit. They cost about $8 each at Home Depot, and the bulbs 5 or $6 each.

Yes you can do plants and keep costs down by staying to low light plants.

Do not buy CO2: a huge cost for pressurized, and DIY is too time consuming and a hassle for what you want to do.

Lighting: Dump the 24" strips. I have the same tank as you. Get 48" strip lights. The bulbs are 40 watt. Either cheap shop lights from a Home Depot type store (Get 2 x 2 bulb fixtures), and attach them into a wood hood, or just buy some All-Glass brand 48" strip lights and put them over a glass top (do you have one of those with your tank?). I believe they make dual bulb strips in 48" length. 120 - 160 watts is plenty.

Plants: Java Fern, most of the Crypts, Amazon Swords, some easy to grow bunch plants, ask your fish store for suggestions.

Fertilizer: A good liquid like Seachem Fluorish or Excel added a couple times a week per instructions. For amazon swords, a plnat-tab or Jobe-spike fertilizer pellet buried in the gravel under the plant.

A little bit of driftwood, a rock or two, and you will have a beautiful tank with very low maintenance plants. I have done this for years and the tanks are beautiful.

Joe, most of the advice you are getting is good.
You have a very nice and expensive tank. I'm guessing that you have the bucks to set it up nicely, but don't have the time to spend fiddling with it all the time.
The most cost-effective way to light it(and you really need to increase that) is to call AH Lighting, describe the tank and hoods you have, tell them you want something in the 2watts/gal. area and they will give you all your options. They are very good in that regard. If you do it this way you'll have to wire it up and mount it in your existing fixtures, which is not all that difficult to do and you will have exactly what you need, light-wise, for the application you describe.
If you don't want to do the wiring, you can buy strip lights at a number of on-line sites, or at your LFS, for a good deal more than the AH option would cost you.
And 2 watts/gal. CF would allow you to stay away from the CO2 thing and still grow low/moderate light plants.
Keep in mind that you will still need to find the balance(fish, plants, and fertilizers) for your particular tank, but once you do, it should require a small amount of time to maintain.
Yes to the Flourite......the stuff is complete and you will not have to add anything else to it.
Yes to the Cannisters. Either one large, or two medium sized would work nicely for you. I would lean toward the two, as cannisters can leave "dead spots" in areas of the tank. You want the water to move. In a tank that size, I don't think one cannister will do the job.
Two of the nicest plants for the lighting you want are Crypts. and Anubia. They both come in all sizes and shapes. Fore-ground, mid-size, and background. Throw in some stem plants for accent and you're in business.
Good Luck,
Len

Ok, back to the drawing board.
Did the tank come with a glass top? You can still get decent CF for it if you want to build your own canopy, which is also an easy project. Go here: http://www.ahsupply.com/
Schroll down to DIY enclosures on the left side of the page. There are a couple of links that will show you how cheap and easy it is to make one yourself. Then you order the lighting and install it in your enclosure. All you'll need is a glass top to sit it on. Or................
The least expensive option is shop lights. Four 40 watt. daylight tubes in a pair of shop lights would give you 160watts of light and that set up would cost about $35 - 40. On a 120, that's going to be a low light situation. In a deep tank like yours, CF is a much better way to go.
What are the dimensions of the tank?

Len

I wanted to throw a couple of my own questions out there because they relate. Do the cheap Home Depot shop lights use the same size flourescents? Can I use the flora-gro or similar bulbs? Also, do I need a glass cover or something over the top of my aquarium? I am thinking about building my own cover for a 20 gallon with a 2 bulb shop light over it.