SpeakerClock ($0.99) provides a bright easy-to-read display showing you exactly how much time you have left to present your paper and take questions. It's a deceptively simple application full of lovely little design touches. I used it at a recent conference and found it an absolutely valuable tool to have around.
This app works well both on the iPhone and the iPad -- as a conference organizer, it's really great to use the iPad's larger screen from across the room. As a speaker, the iPhone version works particularly well when placed on a small business card stand on the speaker's podium.
Want to easily share your contact information? Contxts offers a simple solution. You can sign up for a free account at contxts.com, where you can enter your details. Anyone with a phone (it doesn't have to be an iPhone) and an SMS plan can text a short phrase (like "demotuaw") to 50500 and they'll receive the information you set up at their website. Their free iPhone app lets you edit that information directly. What's more, when you turn the iPhone on its side, you can display a "HELLO my name is" contact sheet that instructs people how to retrieve your contact data. What's great about Contxts is that it's a solution that works with any group of people, whether they've hopped onto the Apple iPhone train or not (of course, if they have an iPhone or an Android phone, there's always Bump).