Of course this will depend on each person's historical knowledge of the actual events.
To start things off i will offer the Battle of Britain and Waterloo.
The BoB had an number of small errors; Mk IX spitfires not Mk I, Spanish built Heinkels with the wrong type engines, same goes for the Me 109's but these were all that were available. The lack of other german aircraft such as Ju 88's, Me 110's and Do-17's was also a disappointment but understandable.
That said, while the actual account of the battle was simplified a bit, for both time constraints and clarity the events were portrayed fairly faithfully as to what happened during the real BoB and the air combat scenes were very realistic, to the extent of my knowledge as to what it was really like, anyway. Just a few too many exploding planes.
![Wink ;)](./images/smilies/icon_wink.gif)
Waterloo: while again the events were simplified a bit it also fairly accurately outlined the events of the battle. Uniforms were beautiful and faithfully duplicated (to my eye anyway) and battle scenes were acted out in a manner representative of the time period (contrast this with very inaccurate battle sequences in more recent movies like Alexander and Gladiator where sizzle, not historical accuracy was paramount). First rate both as entertainment and as a history lesson.
There are other good ones and a lot of bad ones...but i'll leave those for someone else..