A lot of famous folks have (or have had) interesting, or surprising, in-laws. Probably the all-time best example is when Michael Jackson briefly married Lisa Marie Presley, so his father-in-law was Elvis!
Other examples:
Jack Black’s father-in-law is jazz legend Charlie Haden.
Joel Madden (of Good Charlotte) has Lionel Richie as a father-in-law.
As Hollywood is pretty inbred, there are lots of other examples. Which are the most interesting or surprising?