There are a remarkable number of good old books available in whole or in part at Google Books. Here is a list of a few that I have come across recently.
I'll begin with the what seems to me to be the gem of the collection (links are to Google Books except as noted otherwise):
Ridgley, Thomas - A Body of Divinity, being the substance of Lectures on the Larger Catechism (vol. 1)(vol. 1 - second copy); (vol 2)(vol. 2 - second copy) (pdf/txt/main from Archive); (vol. 3); and (vol. 4)(vol. 4 - second copy)
Watson, Thomas - A Body of Practical Divinity, Consisting of more than 170 Sermons on the Shorter Catechism, 4th Edition (link)
Tenison, Thomas - Popery Not Founded on Scripture (vol. 2)
Usher, James - Eighteen Sermons Preached in Oxford (link)
Gillespie, George - Treatise of Miscellany Questions (link)
Charnock, Stephen - Two Discourse: Of Man's Emnity to God; and Of the Salvation of Sinners (link)
Sedgwick, Obadiah - Humbled Sinner Resolved what he should do to be Saved (link)
Beveridge, William - Theological Thesaurus (link)
Mather, Samuel - The Figures or Types of the Old Testament by which Christ and the Heavenly Things of the Gospel were Preached and Shadowed to the People of God of Old (link)
I cannot vouch for every word of each book, but they are generally books that have proven their worth over time.
Sola Deo Gloria!