Of course this whole thread belongs in "books and media" but I'll bite.
Off the top of my head without internet cheating
Fatherland is the most obvious example of a traditional AH book turned into a film, and its not that bad at all.
The Final Countdown is really more of an ISOT than AH but it works.
Peggy Sue Doesn't Live Here Anymore and the Back to the Future series can have obvious AH elements, especially BTTF.
Inglorious Basterds certainly creates an alternate WW2 at the end, but I really would consider the entire movie more of an anti-Nazi revenge fantasy.
There are a number of fantasy and SF films that certainlly can be seen as occuring in an alternate time line, such as Brazil or Sky Captain and the World of Tomorrow.
Sliders, the TV show, is about the best example of AH to hit regular (American) TV, although as mentioned by another poster if often failed to live up to its promise.
I'm really not sure whether or not to consider CSA a true piece of AH. Superficially it is, but the film is really just a satrical polemic on race relations.