I've been exploring hydroponic gardening lately, and thought y'all might be interested in hearing about my setup:

Materials

1 Footlocker or trunk, bigger is better.  
1 Rubbermaid dishpan that just fits on the bottom of the trunk, when the trunk is turned on its side (this will make more sense in a few minutes, I used a 12 quart one) 3-4 blocks of FLORAL FOAM (Preferably agricultural grade, as it does not have preservatives in it, but Oasis will do if it is completely rinsed/soaked first) 1 Muffin Fan (look in computer surplus stores) 
1 50 WATT High Pressure Sodium lamp (Or your lamp of choice) 
1 roll of tin foil

Comments on Cost 

If you bought all this stuff, it would run about 100 bucks... However, I got my trunk at a yard sale for $5, had the fan lying around, and through some creative scrounging on a public bike trail late at night, came up with the HPS lamp and ballast for free.  The dishpan came from a 'Everything's a dollar' store, and foam is cheap... I think I spent $30 total (including fertilizer, which I will discuss later)

First, cut the handle off of one end of the trunk, then stand the thing up on that end.  Sitting it on a phone book with the door hanging off the end makes it much easier to open and close. Then install the fan... I put mine on the top of the box, but It could go in the top back corner if light leakage is important.  A good deal of light will be exiting the fanhole (well, more than anywhere else)... keep this in mind.  I also painted the fanblades white in an attempt to reflect the light back into the box, but Im not sure if it worked... it probably isnt necessary. Put some intake holes along the bottom of the box, these will be covered with foil later, so not too much light will be leaking out. Cover the entire inside of the box with foil, excluding the fan area, and where you plan on installing the lamp.  I used duct tape to affix it to the walls/door, and I LEFT IT UNATTATCHED AT THE BOTTOM so air could come through the intake holes. Install the lamp!  I put mine at the very top center of the door, with the bulb sticking straight out, so it enters the rest of the box when the door is closed.  This made it easier to wire, but In the future, I would put it on the back wall of the box, as less of your room will be illuminated when you open the thing (it's kind of like opening up the sun). 

Thoughts on Lamps

According to Ed Rosenthol (believe him if you want to, ignore him if you dont) HPS lamps are some of the best growing lamps made, especially when efficiency is an issue.  These lamps give off an amberish glow, and are often used to light parking lots, bike trails, etc.  They operate on a very high voltage, and require a transformer or ballast to work.  Metal Halide lamps (used in photographic and theatrical lamps) are smaller, and much whiter, and usually do not require ballast, but they use up a hell of a lot more energy.  I used a Flurescent to sprout the plants, and switched to HPS after they had developed 3 sets of leaves (about 48 hours after germination) This was acceptable. Next, it is time to deal with the foam and plant.  I soak the foam overnight in a nutrient-water mixture (more on that later) after rinsing it extremely well.  Then I cut a brick or 2 into 1" cubes, and plant one seed in each cube.  Planting in foam means you place the sead on the foam, and push it in with a small wire or something similar, so the seed is surrounded as much as possible by the wet foam.  The cubes are placed in the dishpan, and 1/2" of water-nutrient mixture is added to the pan.  The foam will suck up water and nutrients as necessary, so it is important to try to keep the water level at about 1/2".  It is better for the water to be slightly too low (but not dry) than too high 
The seeds can take as long as a week or 10 days to germinate, do not worry if nothing happens at first, and it seems that I never get more than about 15% of my planted seeds to sprout.  This suggests a fault somewhere in my system, but I havent identified it yet, no do I especially care.  I just plant a LOT of seeds, and then use the best seedlings for my gardening.  Usually a smoking-buddy or someone will take a free marijuana seedling off your hands with a minimum of hassle. About 3 days after germination, a few pairs of leaves should've formed.  Now is the time to transplant.  And transplanting is the glory of foam.  All you need to do to transplant things growing in foam, is put the small block of foam (with the plant in it) on top of the larger block , and rub them together a few times.  The roots will grow out of the small cube, and into the bigger one in a matter of days.  I managed to find foam in 12" cubes... cutting these in half gave me 2 pieces of 12"x12"x6" foam, and each of those can easily hold one plant, probably 2.  I personally grow only one plant in each trunk, but 2 smaller ones are probably perfectly acceptable.

Lighting 

When I transplant is when I turn on the HPS lamp.  It then stays on for 24 hours/7days until the plant is 8-15 inches tall.  Then it is time to force flowering.  This can be done by giving the plants a 10-16 hour dark period in each 24 hour day (this should be done using a cheap timer like people use when they go away on vacation in an attempt to foil burglers) In a matter of 3 weeks, sex should be apparent on the plants... REMOVE THE MALES.  Keep the dark period constant until it is time to pick, dry and enjoy.

A word on water-nutrient mixtures

Floram foam should be totally inert, meaning it does not provide the plant with ANYTHING except something for the roots to grow in.  Thus all nutrients that the plant would get from the soil MUST be in the water.  Read a few books on hydroponics to figure out what mixture suits you best, I personally use a liquid plant food that shows on its label an N-P-N count of 10-15-10.  This seems to work fairly well for me.  I know people who use 20-20-20, and quite a few who use different foods during different stages of growth.  Read up on the subject and decide for yourself. Anyway, this was not ment to be a 'HOW TO GROW WEED' type of post, but apparently it has become one (sort of).  It was ment to talk about my grow room, as it was described earlier in this post.  I have found that a single plant can grow to maturity without any trouble in this space, and 2 smaller plants (forced to flower at about 8 inches, instead of the 10-12 that I personally use) would probably be ok too. This grow room is very portable (unplug it and take it with you) clandestine (it looks like a trunk to me (not an uncommon thing in a college dormatory if you are a student), and it can be locked with a padlock) and effective (trust me!) I assume one could grow using standard soil and such in this thing, but I have had great success with foam, and it is much easier to keep it watered.  Rockwool has been sugested to me as a medium, but I dont even know where to buy it... apparently it is much like foam in that it is inert, and transplanting is a breeze.