In Beyond the Woodshed, I mentioned the generally unexplored point that Stella Gibbons' Cold Comfort Farm is set in what has now become an alternate history, a 1950s with videophones, routine use of aeroplanes for personal transport, and past "Anglo-Nicaraguan wars of '46". I like the alternate-history genre a lot, and tidying the office, I found a book I'd forgotten, Back in the USSA by Eugene Byrne and Kim Newman (Mark V. Ziesing, 1997, ISBN 0929480848).
Back in the USSA is a paste-up of a cycle of stories taking as its premise the idea that the 1917 Communist revolution took place not in Russia, but in the USA, led by activists such as Eugene V Debs. The scene is set by In the air placing Buddy Holly in the 1989 Soviet America, followed by a series of vignettes, Ten Days that Shook the World, telling the course of the revolution 1921-1917. Other stories include Teddy Bears' Picnic, a dig at the tropes of the US Vietnam War mythos by showing English comic characters conscripted to a British Indochina war; in this reality, Apocalypse Now becomes a very English It Aint' Half Hot, Mum ("I love the smell of burning flesh in the morning; it reminds me of cooked breakfast!"). Citizen Ed (1945-1984) tells the story of Ed Gein, who is allowed to continue his activities because, as in the real-world Soviet Union, serial killers officially don't exist. Abdication Street (1972) is a Tsarist retelling of the Charles-Diana wedding, and On the Road (1998) is a Kerouac-style journey through a post-Communist America satirizing the tycoon Robert Maxwell.
The tone is mixed, from outright comic to serious; but it's hard to take 100% seriously a work that cheerfully mixes real-world characters such as L Ron Hubbard, McCarthy, Capone and Lindbergh with fictional ones such as The Waltons, Tom Joad from The Grapes of Wrath, the Likely Lads, Nigel Molesworth and Pavel Chekhov. It's further lightened by many in-jokes and cameos, such as Kenneth Halliwell as a successful agent with Joe Orton as his wannabe-playwright assistant, and a Hitchcock film called Nutter, set in Skegness, starring Margaret Rutherford and a Lithuanian unknown called Larushka Skikne (Hitchcock's career suffers because he is never forgiven for the scene in which Sylvia Sims is murdered in a bathing-machine). The overall flavour, then, is satire in which the reversal holds up a mirror to real-world history.
If you like this kind of alternative-history-meets-pastiche, the journalist and novelist Kim Newman excels at it. I also recommend his series of Dracula novels, starting with Anno Dracula, which plays out Victorian and post-Victorian history along a timeline where Count Dracula, not Prince Albert, became the Prince Consort of Queen Victoria. See The Official Kim Newman Web Site for background. Newman and Byrne also maintain an Alternate History Pages site, where they keep notes and material relating to a projected series, The Matter of Britain, set in a Nazi-dominated Britain. It's not a new premise (compare Brownlow & Mollo's film It Happened Here, Len Deighton's SS-GB, Keith Roberts' short story Weihnachtsabend, Robert Harris' Fatherland, and many many others - see The World Hitler Never Made). However, their take ought to be worth reading if Byrne's The Glimmer Man is anything to go by (a story about Nazi-occupied Britain from the viewpoint of Bristol inhabitants, commmissioned for Bristol's bid for European Capital of Culture 2008).
A good many Kim Newman stories are online elsewhere: see the links at Wikipedia for stories set in a variety of alternate histories (some possibly offensive): Coppola's Hearts of Darkness with vampires; the McCarthy witch-hunts actually hunting witches; a Hollywood history as it might have developed - with well-known classics as grossly sexual explicit versions compared to the ones we know - if there had been no Arbuckle scandal leading to the Hays Code; and so on.