There is a big difference between alternate universes and alternate history. Alice fell through the rabbit hole into an alternate universe. Robert Silverberg explored the ramifications of alternate history in Up the Line. One lets you go anywhere from the starting place of the "real" Earth (or whatever planet you started on); the other is bound by the strictures of actual history. These are examples of alternate history:

• Seventh Son by Orson Scott Card, the first in a series about Alvin the Maker. The others are:

Red Prophet
Prentice Alvin
Alvin Journeyman
Heartfire

• 1632 by Eric Flint, which takes the reader, and a whole West Virginia town, back to the Thirty Years War.
  
• The Lord Darcy series by Randall Garrett, which gives us an England still ruled by the Plantagenets where magic is commonplace:

Lord Darcy
Lord Darcy Investigates
Murder and Magic
Too Many Magicians

• The Guns of the South by Harry Turtledove, in which a friendly time traveler offers advanced weaponry to Robert E. Lee
  
• The Worldwar series by Harry Turtledove, with aliens invading the midst of World War II

The following are "straight" alternate histories and so not really what we support, but interesting reads:

• Bring the Jubilee by Ward Moore

An acclaimed "what if" the South had won the Civil War by winning at Gettysburg, re-imagining the entire fate of the American continent.

• Redcoats' Revenge: An Alternate History of the War of 1812 by David G. Fitz-Enz

Most people really don't know how close infant America came to ending up back in the British Empire in 1814. Suppose England had unleashed the Duke of Wellington on the hapless American army?

• A Traveller in Time by Alison Uttley

This gentle YA story about an English girl who spends her summer wandering backward to Elizabethan times at the very old manor house where she lives is poignant and haunting. She comes to know some of the people involved in the plot to try and free the imprisoned Mary Queen of Scots, and so forever will regard them as something more than names on the pages of her history books.

You can purchase Alternate History titles through the Other Worlds Bookstore.