Here's the schematic. I thought there was one like this on here already, but I couldn't find it. R11 is variable so you can adjust the speed, 14hz (not 140hz, .gif uses 100th's instead of milliseconds, oops) is about in the middle of the span. I show two sets of two LED's, but you could put several more on each of those transistors (if you want to make it brighter) just add more LED's + 220 ohm resistors on each side like that. The cap voltages are anything above 6v. I suggest 4 AA batteries because that will last longer than a 9V, but you could use AAA's or whatever. The 4017 is counting down from the top in a round-robin fashion, so it's right side on, off, right side on, off, off, left side on, off, left side on, off,off, repeat.