Magic Loop is my favorite.
I just came back from Camp Stitch-A-Lot in Davison, MI which is a cross-stitcher's get together. Having just learned how to knit, I was more interested in practicing my knitting. A lady at camp (who also knits) saw me fighting with my sock recommended the Magic Loop. I was soooo frustrated fumbling with dpn's and two circs that I almost gave up on socks entirely. When she recommended Magic Loop, I left immediately to the nearest yarn store and bought the book and a set of Addi Turbo circular needles. I spent the next day and a half doing nothing but practicing my rib stitch in the round for my first pair of socks. I am in heaven!!!
Basically the magic loop is knitting in the round using one circular needle. Half the project is on the points and is the part being worked on. The other half is in the middle of the loop of the circ. There's enough slack in the loop on either side to allow for movement of the points, so it kind of looks like the knitted project has Mickey Mouse ears. The book I bought recommends a minimum of a 32" cord but 40" or above is ideal.
Edited to add the YouTube tutorial: http://www.youtube.com/watch?v=BtBSmxGomPk