The secret structure of great talks http://www.ted.com/talks/nancy_duarte_the_secret_structure_of_great_talks.html Really enlightening TED video. See the structure underlying both 'I Have a Dream' and the 2007 iPhone launch talk.
Speaking for Hackers http://www.speakingforhackers.com/ An in-progress ebook of tips. Covers end-to-end from proposing to planning to speaking.
The Art of Speaking http://tekpub.com/productions/ft_speaker Watch a respected speaker prepare a talk from scratch in 90 mins. Lots of great advice.