Well - there's a couple of things here that you might be referring to depending on how involved you are thinking on getting. The following are the most popular units for this type of thing.
I think that you are referring to an automated system like I have: http://www.bigrhythmwine.com/gearheads/MikeY.htm
Here's the components:
This thing allows you to have your effects always bypassed until actually activated by an external footitch. They also sell a midi footswitch for it - although several other types are compatible with it - http://www.voodoolab.com/gcontrolpro.htm
This footswitch can also control other midi switchable units as well as accepting inputs from expression pedals and lots more. It is programmable so that with one button you can turn on/off one or several effects depending on how you preset it.
With this type of setup, your effects would usually be located in a rack somewhere - not actually on the floor. This would offer you the freedomm to adjust the effects while playing without having to bend down to do so.
Even used these components are going to run you a bit of cash - the switcher and foot controller will be about 600 if you find a good deal on ebay. Then you'll need to figure out some kind of system to rack all of these components and effects. You'll also probably want a power supply for all of your effects too - like this one: http://www.voodoolab.com/pedalpower_2.htm
So, all in all, you could easily be looking at about $1000 to set this up.
The other option is to go with a pedal board on the ground - like this: http://www.pedalpad.com/images/examples/Gary-Southern-CA-XLs.jpg
These boards will run you about $300 new and it's all you'll need. It comes with a power supply for all of your effects and it's very customizable. It's also very compact and convenient and super easy to set up at gig time. Open the box, plug in & go.
For most situations now I go with the pedal board instead of the big rig because it's just easier to set up, tear down, transport, carry up stairs...