It's hard to go wrong with Calvin. His sermons are treasures of practical teaching and Christian living, his polemical writings are deep and thoughtful, and his commentaries are still something of the standard for biblical exposition. He has long been my favorite author (and not just because I'm a calvinist!)
Brooks is likewise clear, fresh, and practical. Always a pleasure.
Edwards and Owen are very good but tend more toward the "brainy" side of theology. The more I read of it the more I appreciate the "simple" encouragement for the Christian as opposed to controversy.
Ryle is one of the clearest and most endearing theological writers of the 19th century (the dark ages of writing and typography )
Henry is great and I have benefited much from him. His style is much more "applying" than "expositing". Bunyan is similar, but I find I can only take so much of his style from his general writings. He's more flowery than I'm used to and seems better in smaller doses.
Flavel I have read little of, but I know Archibald Alexander encouraged his students to read him completely through.
Many greats have already been cited, so I won't repeat them.
Where are the Princetonians? Warfield was mentioned (and Alexander, offhandedly), though neither Miller nor the Hodges. I would also add Vos and Machen.