Present From Your iPhone/iPad By Transmitting To Any Projector-Connected Computer: Air Projector for iOS | Presentation Tools |

From the official site: "Leave the VGA dongle at home. Project PDFs and photos directly over WiFi.

Air Projector projects PDF documents and photos wirelessly from your iPhone or iPod Touch to a browser connected on the same local network.

No additional client software is required.

Just fire up Air Projector and type in the displayed URL in your web browser.

Then flip through the pages or photos on your iPhone and the remote display updates automatically.

-> Tap and hold to show a laser pointer on the remote screen.

-> Send PDF documents from Mail, or a third party document manager such as Dropbox, to Air Projector to present them.

-> Works great with exported PDFs from PowerPoint or Keynote (note: transitions and animations are not stored in PDFs).

-> Share presentations with remote colleagues via online meeting or desktop sharing software (such as iChat).

Note: Air Projector requires iOS4.0 and above."

You can even use Air Projector peer-to-peer with a computer via an ad-hoc network when a WiFi hotspot is unavailable.

Download on iTunes: ($0.99)

Free version also available (to test and verify if you like what this app does):  

Find out more: 

(Thanks to Ana Cristina Pratas for discovering this one)