On the Trinity - E.W. Watson translation. Each of the twelve books in its own file, with notes and links to contents, previous, next. - http://www.ccel.org/ccel/schaff/npnf209.ii.v.html
On the Councils - L. Pullan translation. With notes. If you wish to read an introduction, use the link for "previous". From the Nicene and Post-Nicene Fathers of the Christian Church, second series, vol. 9. - http://www.ccel.org/ccel/schaff/npnf209.ii.iv.ii.html