Here are some titles of selected shorter writings for your library:
(1) Collected Writings of William Still vol 2: Studies in the Christian Life. This volume is valuable for its focus on the cross and the benefits of salvation. There is a great section at the beginning of the book on three dimensions of the cross. What you get in this work is a collection of writings by a man who had great insights into the Scriptures. Still’s pastoral heart is manifest by his use of Scripture and desire to apply it to Christians for their growth and development. Both Sinclair Ferguson and Eric Alexander speak of William Still as being a spiritual mentor. This volume is particularly worth having and reading.
(2) Philip Henry Christ All in All. Philip Henry was the father of the great Presbyterian commentator Matthew Henry. This volume is a compilation of sermons and meditations on our Savior. This is both a work of short writings and a magnificent work of Christology that should be on your shelf. The book is not easy to find, however, you can sometimes find one of the internet for approx. $20-30. It was republished in 1976 by Reiner Publications. Four of the chapters out of the book are available here. For a good biography of Philip Henry you can download one written by his son here. You can dowload his Diary and Letters here. You can also dowload his Remains here.