If you have an eclectic group of frames, including some circular ones, you'll have to come up with your own arrangement. Confine your display to a specific area, like in a rectangle over your mantel, so it's easier to create a unified look.
Cut out smaller replicas of your frames using graph paper, with one square corresponding to one square inch on your frame. Arrange your paper replicas in different designs, trying many options, to find a symmetrical arrangement. It's easier to create symmetry with the largest frames first, working your way down until your smaller frames fill in the empty spaces left over.