Picture Books:
The Eleventh Hour: A Curious Mystery by Graeme Base
The Web Files by Margie Palantini
Nate the Great series by Marjorie Sharmat
Detective LaRue by Mark Teague

Chapter Books:
Encyclopedia Brown by Donald Sobol
Brixton Brothers by Mac Marnett
Jigsaw Jones Mysteries by James Preller
The Fantastic Secret of Owen Jester by Barbara O'Connor
For something different try these older titles.
Stories to Solve: Folktales from Around the World and More Stories to Solve: Fifteen Folktales from Around the World, both are told by George Shannon and illustrated by Peter Sis

In each entry, many are one page in length, Shannon sets up the story and then asks readers to solve it.
In a "Dri

"What did the crow do? Find out the answer on page 20.