OK, as the self-proclaimed resident expert:
Parallelities- Alan Dean Foster
Damn near anything by Harry Turtledove. Start with The Guns of the South.
SM Stirling's Nantucket Trilogy. Start w/Island in the Sea of Time
Also, his novels The Peshewar Lancers and Conquistador
Pavane by Keith Roberts
My personal fav: 1632 by Eric Flint(and all the other books in that "universe") go here:
http://www.crucis.net/ericflint/
Stephen King's new book
11/22/63
Paratime by H Beam Piper. Also, his Lord Kalvan of Otherwhen and the sequel by Roland Green
The Worlds of the Imperium(and sequels) by Keith Laumer
The Big Time by Fritz Leiber
The Timeliner Trilogy by
Richard C. Meredith (Awesome multiverse theory application in this one-and lots of sex and death too.)
The Gate of Worlds by Silverberg
Fatherland by Robert Harris
The Proteus Operation by James P Hogan
The Axis of Time trilogy by John Birmingham (lots of fun)
The Lord Darcy books by Randall Garrett
That should keep you busy.
also, you can go here:
http://www.changingthetimes.net/samples.htm
and I suggest reading A Time For Patriots on that site. As well as that author's other work. (Hamilton)
ed.- I almost forgot Mike Resnick edited a series of short story anthologies.
Alternate Generals
Alternate Kennedys (You HAVE to read The Winterberry!)
Alternate Presidents
etc