In Julie Taymor's film version of "The Tempest" (now in post-production), Helen Mirren, in a gender switch, plays "Prospera."
See a recent interview, "Helen Mirren Talks About Playing Prospera in The Tempest" (ScreenCrave.com, Friday, January 8, 2010, 4:50 PM, By Mali Elfman)—
"With Prospero you can change it into a woman without changing much of the text, very little of the text has changed, only at the very beginning— the backstory. In fact, one of the most famous of Prospero’s speeches, it’s an invocation— brilliant, fabulous speech— is actually from 'Medea,' almost lifted lock, stock, and barrel from the play 'Medea' and it’s Medea’s speech and Shakespeare just took it. It’s incredible. Like three words have changed. So it’s actually a woman’s speech."
It's actually not from "Medea" (the play by Euripides), but rather from the version of Medea in Ovid's Metamorphoses, Book 7.
Related material: Blurring the Lines and Mutatis Mutandis.
See also Tuesday's entry on Taymor and theatre.