If you give presentations regularly, go right out and get a copy of "Made to Stick" by Dan and Chip Heath. I am half-way through the book after reading it for four hours because I am A) making notes on almost every page and B) stopping to work on ideas for my presentations that the book has sparked.
Buy it on Amazon
The Made To Stick web site
If you aren't ready to buy the book, then at least download this free manifesto from ChangeThis. The manifesto, written by the brothers Heath, is focused on strategy, but it discusses many of the key learnings from the book.