There are a lot of sites with useful advice out there. This post is intended to collect several links for future reference.
Technically Speaking – Videos of math research students presenting their findings. I love the examples of bad style along with good style. This comes out of an NSF-funded project.
Joe Gallian’s Advice on Giving a Good PowerPoint Presentation from his article in Math Horizons.
Giving a Conference Talk by Mike Dahlin.
Oral Presentation Advice by Mark D. Hill, includes “How to Give a Bad Talk” by David A. Patterson.
Giving an Academic Talk by Jonathan Shewchuk.
I also have several resources on good mathematical writing that I’ll share later.