The first of Eric Flint's series of books about a 20th-century American town catapulted back through time to 17th-century Germany. Equal parts science fiction, historical romance and political thriller, Flint's writing is superby detailed -- it's obvious that he's done his research on any of the wide range of topics he chooses to write about -- and great fun to read.
Available online from the Baen Free Library.
ISBN 0671319728.