Many people like to get a book with devotional readings for the entire year. If you are shopping for an annual devotional book, the two classic, all-time best, in my opinion, are Experiencing God Day-by-Day, by Henry T. Blackaby and Richard Blackaby, and My Utmost for His Highest, by Oswald Chambers (I recommend spending a little extra to get the updated edition of Chambers, because his work was originally written in 1917, and the language of the original can be difficult to follow.) Both of these devotionals are strongly rooted in the scripture, with penetrating insights that will drive you to deeper prayer and faithfulness.
Another excellent classic, Morning and Evening, by Charles Spurgeon, provides readings for morning and evening every day. A Year with C.S. Lewis provides great selections from Lewis’s writings for every day of the year. The Songs of Jesus, by Timothy Keller, has a year of brief, Christ-centered daily devotionals through the Psalms. The prayers Keller offers are particularly inspiring. Keller has also published a new devotional on the Proverbs, God’s Wisdom for Navigating Life. All of the above devotionals will cause you to think deeply and inspire you.
Jesus Calling by Sarah Young is an extremely popular devotional that uses the literary device of speaking to the reader as if it is the words of Jesus Himself. The devotionals in Jesus Calling are brief but quite encouraging, especially to those who need to find peace in their lives. However, the devotional has been criticized because the author claims she received the messages directly from Jesus, and some authors have pointed out minor errors in her book that prove not all messages were directly from God. (For more on this controversy, check the excellent book review by Tim Challies here.) Despite these criticisms, I think her devotional is very helpful, and to her credit, Young includes scripture references at the end of each devotional. Young also has published spin-off devotionals that are similar, such as Dear Jesus.
Daily Guideposts, published annually by Guideposts magazine, include many inspiring stories by a different author every day, and while they are well-written, they lack as much substance as the other devotionals mentioned above.
Voices of the Faithful, edited by Beth Moore, has devotional stories by missionaries.
If you are looking for a devotional for married couples, Our Love Is Here to Stay: A Daily Devotional for Couples, by Tony and Lois Evans, is the best one I have read on the subject. It is well-written, interesting, and full of practical wisdom.