A Diary of Private Prayer by John Baillie
The book contains 64 prayers, 31 days of morning and evening prayers and 2 prayers designated Sunday morning and Sunday evening.
The prayers are wonderfully diverse. They expand what I thank the Lord for and lead me into praying for things I don't normally pray about.
The format of the prayers vary, too. Sometimes Baillie will have you praying through Scripture verses, for instance.
Finally, the prayers are just really well-written.