Well, there is H. Beam Piper and his Paratime and Kalven of Otherwhen
https://www.mobileread.com/forums/showthread.php?t=29745
Not historical, but sort of the results of branches in history happening up to the modern day
Andre Norton had a similar series called Time Traders (a few of which are PD)
http://en.wikipedia.org/wiki/The_Time_Traders
Probably the best is The Man in the High Castle by Philip K. Dick.
The absolute most enjoyable series (for me) was Randell Garrett's Lord Darcy series
Baen has a omnibus of this for $4
http://www.webscription.net/p-255-lord-darcy.aspx
Only one novel, but a lot of short stories.
Again at Baen, there is a series by Eric Flint that is sort of alternative history. It's sort of like a Yankee in King Arthur's Court, people go back in time and change history, not really alternate. But you can read the first one free:
http://www.webscription.net/p-379-1632.aspx