A friend of mine in the business says you can also pick up projectors that will link directly to your iPad, no intermediary devices necessary. Quite convenient for using Keynote I'd imagine, although he tells me the feature has limits on what it can transfer and project (static images and text but not video clips).
This friend is also an IT expert who suggests that a few years down the road, you'll be able to stream presentation notes and graphics to everyone in the audience to enhance your talk. It's a brave new world out there for those with imagination.
Oh, yes, I almost forgot, get yourself a free stopwatch app (there are several different styles to choose from) if you have to make presentations of certain limits (mine are 20 minutes in most cases). You can run it in the background and check on how you're doing time-wise after you practice the presentation. A very useful feature for those of us working ... and delivering ... on a deadline.
For more on using the iPad and its many apps for public speaking: http://jsbrookspresents.blogspot.com/2013/04/public-speaking-engagements-enhanced-by.html