Two books for one credit deal, unless otherwise noted, please request one and pm me for the others.

Agatha Christie (Three books for one credit):
Nemesis
Postern of Fate
The Secret Adversary
Death Comes as the End
And Then There Were None
Murder on the Orient Express
By the Pricking of My Thumbs

Avi:
Who Stole the Wizard of Oz?
Don't You Know There's a War On?
A Place Called Ugly
S.O.R. Losers

Dianna Wynne Jones:
Witch Week
The Crown of Dalemark (Book Four, the Dalemark Quartet)
The Chronicles of Chrestomanci Volume 2 (Contains both The Magicians of Capron and Witch Week)

Jean Craighead George:
On The Far Side of the Mountain
Frightful's Mountain

Scott O'Dell:
Zia
The Road to Damietta

The Claidi Journals by Tanith Lee:
Wolf Tower (I)
Wolf Star (II)

The Dragon Chronicles by Susan Fletcher:
Dragon's Milk (I)
Flight of the Dragon Kyn (II)

Katherine Roberts:
Spellfall
Song Quest

Dan Gutman:
The Kid Who Ran for President
The Kid Who Became President

Romances (Three books for one credit):
Tidings of Great Joy by Sandra Brown
This Magic Moment by Patricia Rice
Bet Me by Jennifer Crusie
Cupid's Meloday by Karen Fox
Tast of Honey by Eileen Goudge
Contracted: A Wife for the Bedroom by Carol Marinelli