Every teacher should have some version of "um speeches" available as the need arises. A twist on the previous activity, this one focuses on "um," "uh," "like," "y'know," and all the other filler words.
Four students go up to the front. (This minimizes the "I'm up there alone" factor.)
The first student speaks by answering a question drawn by the teacher. The moment the student utters a filler word, they're "out," and tag someone else to join the four. The next in line has to continue the thread, or try a different answer to the question. They're also "out" if they successfully answer with some sort of reason and clarity.
You can modify this for different purposes:
Intro / main points / conclusion, one per student (four or five up front, depending on the number of points).
Point / counterpoint.
One delivers good content in a monotone, while the second says the same thing with an exaggerated, histrionic delivery. The third says the same thing "just right."
Having more than one student up there makes a big difference. Rotating through gets everyone involved--and even the reluctant speakers will go and succeed, as long as you have "set the tone" and given them previous practice speaking to smaller groups.