If you ever watch stuff online, on the PBS site they are showing some new Hercule Peroit episodes by Agatha Christie. They rotate what they show so you have to catch it at before it stops playing. But Masterpiece/Mystery always has something, Miss Marple or something. I really love those British mysteries.
http://www.pbs.org/wgbh/masterpiece/ If you go to the top where it says "Watch Video" you can see the shows they currently have up. Some may say "Promo" by them and those aren't full length, just like trailers. Usually the Mystery ones are listed under most watched.
Right now you can see Murder on the Orient Express - it's a new version, better. Plus another A.Christie.