I Heart You, You Haunt Me by Lisa Schroeder
The only complaint I have about this book is that it's really short! Because it's written in verse, it's a really quick read. Still, Ms. Schroeder manages to pack a lot into it.
The book deals with a young girl, Ava, whose boyfriend, Jackson, has died. She is devastated, as she believed him to be her soulmate, and also blames herself for his death. And then he begins to visit her - she can't feel him or see him, but she knows he's there.
As the book progresses, Ava deals with her grief, her guilt, and her confusion about the "haunting." Her inner turmoil is dealt with very well, but that's really all. There's no room for any character development, the death of Jackson is briefly described, and there's really not much of a plot.
Even so, the book succeeds for what it has set out to do, and I definitely recommend it.