Of course the D40 isn't a ring flash ... Marcus asked: "Are there any other, more portable, flashes for the V cam? Not necessarily ring".
By far the best ring flash I've used is the Hensel which is made of carbon fiber so it is very light to hold, and has a handle for hand-held work in studio. As far as I know, none of the pro level, larger ring flashes are self contained and mobile ... they are tethered to a generator box.
The smaller, self contained ring lights available for 35mm cameras, and often used for macro work, throw a small circle of light, are underpowered and wimpy.
Ring lights work because they surround the lens and light fairly evenly, often producing a tell tale drop shadow around the subject and a donut spectral highlight in the eyes. The effect would be lost with a reflector made for the D40.
I suppose you could make a "beauty dish" reflector for the D40 using the Telephoto reflector and adding a center "dot" with a reflector surface facing inward. But I doubt it'd work since the shape of the tele reflector is designed to narrow and focus the light beam.