SPT wire is what I think a lot of us use...myself included. It allows you to create extension cords at pretty much any length you want. There are 3 types of wire out there. SPT1, SPT2 and SPT3. The higher the number the thicker the insulation is on the wire. This in turn will create limits too how much current you can run through the wire. I use all LEDs in my display and even when I didn't I have very low currents on strings so I always use SPT1 wire. I don't think many of use use SPT3, but it is out there. Of course you will need vampire plugs to match the wire you are using. For instance, SPT3 wire will not fit in SPT1 plugs. You can also take the female plugs and snip out the one side and put multiple plugs in a single line of wire. The plugs are very easy to use and allow you to put the wire in, push it against the prongs inside and place the cover on, which holds the in extremely tight.
There are a ton of suppliers out there. Creative Displays, Christmas Light Show, LED Holiday Lighting (buy at your own risk here), Action lighting....blah blah blah.
Hope that helps a little bit.
