Jo Walton did the excellent "Small Change" trilogy with a fascist post-WWII Britain.
Mary Gentle does some very good AU (mostly medieval-to-Renaissance European).
S.P. Somtow has "The Aquiliad", a hilarious AU in which ancient Rome made it as far as the Americas and are being meddled with by time-traveling aliens, seen from the viewpoint of a Lakota chief whose relatives include one "
Equus Insanus".
Speaking of ancient Roman AU, Robert Silverberg has the "Roma Eterna" collection of short stories, in which the Roman empire likewise kept going until space travel.
A lot of historically-set/time-travel-involving sf/fantasy tends to verge on AU sometimes, due to filling-in-the-blanks of the unknown and incorporating the magic/tech.
You can pick up L. Sprague de Camp's classic
Lest Darkness Falls for 50% off
direct from the publisher's website with the discount coupon offered in their monthly free book newsletter: DIR06579, usable on any of their other books, as well.
Hope this helps.