Unfortunately, there isn't a standard for screw hole patterns for base plates. Usually the manufacturer of the base plate will indicate which routers are known to fit a certain plate, and often will offer multiple choices in plates. Sometimes a blank plate is offered so you can drill your own mounting holes as well.
As for which one to consider, currently I am using a generic base plate for my table that was specifically made for the bosch. There are a lot of great choices out there. Just make sure the plate is flat, and will stay flat under the weight of the router, has the ability to put collars on it so the opening isn't too big for the bit, and a starting pin can easily be used.