All from memory, here, so forgive mistakes.
My favorite is from The Tempest (also my favorite play):
Ariel: They are in such a state
Your heart would burst to see them.
Prospero: Would it, spirit?
Ariel: Mine would, sir, were I human.
Other good ones:
Henry IV, part 1 (can’t remember who the first speaker was):
I can call spirits from the very deep!
Hotspur: As can I. As can any man.
But when you call, will they answer you?
King Lear:
Fool: The reason that the seven stars are no mo’ than seven is a pretty reason.
Lear: Because they are not eight?
Fool: Aye, you’d make a fine fool.
The trick being, of course, that the Seven Stars are, in fact, eight.
For longer speeches, my favorites are Prospero’s renunciation of his powers (I’ve memorized from “Ye elves of hill, brook, standing lake and grove…” to “…And deeper than did ever plummet sound, I’ll drown my book”) and Marc Antony’s eulogy of Caesar (“The noble Brutus hath said he was ambitious / If it were so, it were a grievous fault”). But I don’t feel like writing either out in full.