I am becoming curiously addicted to
http://www.rantonen.net/clayhunt/It is an app for iPhone or iPad and is as realistic as any I have seen. The sight picture, albeit with an over and under - sorry, is pretty good and the lead required in the expert category reasonably realistic, as far as these things go.
I managed a 25/25 on the beginner game after a day. The expert categories are harder and the arcade game is fun, with a multi shot auto!
It was my 85 year old father who told me about the app. He'd been playing it on his iPad for a couple of days!
Tim