I second Cate Blanchett as Elizabeth I, though that movie wasn't quite historically accurate.
Hmmm, other good ones:
Geoffrey Rush as the Marquis de Sade in Quills (also not accurate, but what the hell)
Stephen Fry as Oscar Wilde (but don't forget Jude Law's amazing turn as Lord Alfred Douglas either)
Daniel Day Lewis as John Proctor in The Crucible (not accurate again! But still great)
Winona Ryder as Abigail Williams in The Crucible (see above)
F. Murray Abraham as Salieri in Amadeus
Tom Hulce as Wolfgang Amadeus Mozart
Speaking of Tom Hulce, whatever happened to him? The only other movie I've seen him in is The Inner Circle (1992), which I think was made in Russia. Aleksandr Zbruyev's Stalin was great. Much better than Robert Duvall's Stalin (from the HBO movie), even though it was a much smaller role. And Bob Hoskins as Beria makes his Kruschkev look like a buffoon (wait, Kruschkev WAS a buffoon). Why does Bob Hoskins always play prominent Communists?