CFL's - At least 100 real watts per plant, and at least an additional 50 real watts per additional plant.
Use a mix of light for a fuller spectrum. Flower, use a 3:1 ratio of 2700K to 6500K bulbs. Veg is the other way around.
I've vegged and flowered under CFL's, I'm very happy with what comes out of veg, no so much with flower.
So, I'm still vegging with the CFL's that I get from the grocery store, but I've upgraded my flower to HID. 1200W HPS and 400W MH. Getting great results.