I was going to mention Das Boot but others got there first.

Band of Brothers supposedly was very accurate (compared to the book) but there's been plenty of controversy about how accurate the book was (and others by Stephen Ambrose too).

It's a long time since I saw it (30 years) but The Duelists struck me as being accurate sword play - at least they were using proper heavy swords.

I believe Cromwell and Waterloo were pretty accurate too, and The Battle of Britain ("Repeat Please" a great moment!!)