And the Marscon Alternate History Reference List

Combination of suggestions and things I thought of.

Time Well Bent: Queer Alternative History edited by Connie Wilkins
Substitution Cypher edited by Kaye Chazan
The Years of Rice and Salt by Kim Stanley Robinson
The Man in the High Castle by Phillip K. Dick
Fire on the Mountain by Terry Bisson
The Dream Years by Lisa Goldstein
The Anubis Gates by Tim Powers
Black Hearts in Battersea and rest of series by Joan Aiken
The Yiddish Policeman's Union by Michael Chabon
Timeline series by Harry Turtledove
Farthing and series by Jo Walton
1632 series by Eric Flint
Lord Darcy series by Randall Garrett
Ash: A Secret History by Mary Gentle
Lion's Blood and series by Steven Barnes
Stars and Stripes series by Harry Harrison
V is for Vendetta by Alan Moore
Baker Street by Guy Davis and Gary Reed

The Dragon Waiting by John M. Ford

More?