I'm looking into buying a ring (ray) flash for this setup:
For now I only found this one: Ring Flash O-Flash for Canon 430EX II. Which is compatible with the setup mentioned above but reviews aren't that good. So I'm looking for suggestions from users with the same kind of setup.
Ring flash adapters for "normal" flash guns (speedlights) come in two basic configurations, which can be described best, I suppose, by referring to the two big-name brands.
There's a fixed-size adapter that attaches to a flash sitting on your camera's hot shoe, like the Ray Flash Adapter, and that needs to fit both your flash head (so it can clamp in place) and the distance between the flash head and the center of the lens (so that the camera can shoot through the center of the ring -- otherwise you get an obvious direction bias to the shadow pattern, and you're restricted to lenses with smaller diameters).
With a Ray Flash-type adapter, you need to find a model that mounts to your flash (if it claims to fit every flash ever made, it'll probably fall off constantly), and that is the right length for your camera/flash combination, within a couple of millimeters. Even if you don't plan to spend your money on the actual Ray Flash, you can use their website to get an idea of the dimensions you're looking for. Again, if the size is adjustable, something had to be compromised, so it will either lose efficiency (something you can't afford to lose much of with the 430EX) or will be mechanically unstable.
There is also a class of adapters that mount the flash on a bracket (attached via the tripod socket) below the camera, like the Orbis. Since they don't depend on the flash and camera dimensions (the flash is pointed straight up into the adapter, so the attachment doesn't need to be quite as secure, and the bracket/arm is adjustable without affecting the light path), it can be a one-size-fits-all sort of solution. At the same time, it can be more awkward and can make using a tripod more difficult. By the same token, though, it's easier to mount the flash separately to something like a Magic Arm/Super Clamp so that you can use an L-bracket or a tripod collar on a lens to rotate thee camera without affecting the mechanical stability of the flash setup.
I can't give you any specific off-brand recommendations, but that should give you enough information to do your own research and shopping.
The ring flash in essence is supposed to substitute for a flash. The ring flash mounts directly to the hot shoe. If you need a second light I recommend using a flash stand alone - a light stand!
Ring Flashes are also not camera specific - Not Brand Specific (not usually to my knowledge) they have different sizes.
A few options other than @dpollitts suggestions are:
