I'm using B&M dynamo powered front light (an Eyc and a Cyo) on two of our bikes and currently have them mounted at the fork crown using the stock mounting brackets. This causes a large shadow from the front wheel that we both don't like. So, I'm looking for racks that have a provision for mounting a light (these lights have a 10mm wide mount that takes a bolt running perpendicular to the beam axis). Does any one have suggestions?
Typically, mini front racks have the type of mounts you are looking for. You will also likely need an arm to hold the light otherwise you will have to mount the light upside down, which the B&M is not designed to do.
A number of manufactures sell these type of racks and arms. The racks will typically have a number of mounting points around the rack, mine happens to have five, two on each side and one in the front (which could use the same mount as the fork crown mount, but this would also expose the light more to knocks and bumps).
In the attached picture my rack is mounted quite low to the tire (so I can attach the fender to the rack), and the light is mounted low below the rack so I can fit a bag on top of the rack without interfering with the light. As a result the pictured setup gets a slight shadow to one side. You could mount the rack and light higher which would likely eliminate most if not all the shadow. You could also mount the arm holding the light to the front set of mounts on the rack which would move the light farther forward again eliminating a shadow. I chose to mount in close to the rack to protect the light at the cost of a slight shadow.
Finally, my fork has an extra set of braze-ons for these types of mini-racks. There are other types of mounting options so you don't necessarily need this braze-on to use this type of rack (e.g., via p-clamps). Some front pannier racks also have a platform like the one pictured built in, so you can use the regular mid-fork mounting point.
The rack I ended up getting was the Racktime Top-It. It mounts the light on the centerline in front of the rack just below the top deck of the rack. This is pretty much where Peter White says the light is designed to go. There is just enough room to mount a B&M Cyo, a bigger light probably wouldn't fit. The location is good, it pretty well eliminates the shadow of your front wheel.
Here's a photo from EcoVelo that shows the rack and light pretty well. On a Kona Sutra the rack mounts a bit lower and further forward (to get the rack deck level). I ran the wires up the diagonal strut inside a length of aluminum tubing to protect them from the pannier hooks.