Well, here's a photo tutorial for a stretchy cast on that I like to use for socks and mittens. It produces in a decorative and elastic edge. This is a little different from the other photo tutorials I have seen. I hope it helps!
1. Make a long tail---3 or 4 times as long as the completed cast-on edge. I use 4 times for a shortish cast-on. For long cast-ons like the lower edge of a sweater or crescent shawl, I measure out 3 times as long, then add another couple arm lengths. 3 times is standard, but I find for my knitting it's often not quite enough.
Put the yarn over your needle with the long tail in back.
4. Turn your palm so it faces up.
(This is a little like playing Cat's Cradle.)
...grab the strand draped over the index finger...
7. Let go of the thumb circle....
...and prepare to start again at Step 3.
Repeat Steps 3 - 7 until you have the desired number of stitches.