 I think it could still use some cleanup.  First, some of the terms used for identities do match the terms used for the same identities on the List of trigonometric identities page.  Ideally, I think this page should match that one, with the proofs linked between sections.  Also, the typesetting of the formulae does not match.  Look at the equations in the angle sum section for details.  Finally, there is inconsistent layout between sections.  For example, the Eulerian proof in the Angle sum section is thrown in to the sum section.  It seems to me it should really have its own (at least sub-) header to separate it, as is done for other identities on the page.    