Delighting in the Trinity by Michael Reeves.
It’s a feeling every reader knows and loves, and perhaps especially the reader of theology. It is the feeling that comes as you read a book and find yourself thinking “This could change everything.” There are some books that go straight to what you think you know, what you are so sure of, what you’ve so carefully constructed, and begin to pull it all apart and to replace it with something that is so much better, so much loftier, so much more worthy of God. Michael Reeves’ Delighting in the Trinity has been one of those books to me. After ten pages I was hooked, after twenty I was reeling and after fifty I knew I would have to go back and read it all again.
The Deep Things of God by Fred Sanders
This is a difficult but beautiful read
The Forgotten Trinity by James White
This is an excellent, slightly technical book.
The One True God by Paul Washer
Though not specifically on the Trinity, this workbook-style book will draw you to Father, Son and Holy Spirit.