I found this one on the net somewhere quite a while ago- can't remember where. Made a prototype on the breadboard though- it works well, just as it looks here. You can vary the fade frequency quite a bit if you want it to go faster, or even slower than you see here. The primary RC constituents are the 5.6K resistor and the 330 ohm cap. Also, the series diodes may be replaced with an appropriate Zener..
