For the general effect of dragons on their surroundings, I'd go with Dragonslayer and Reign of Fire. Yes, both are incredibly bad, but they're about the best dragon-as-powerhouse movies out there.
For the flashback effect, and a good sample of alternate times, you can't go wrong with the original Highlander movie.
For the whole "magical modern age", try to hunt down Cast a Deadly Spell. An impressive film taking place in 1930's Hollywood USA where the whole society has known magic for ages.
Anybody else have other suggestions?