Raoul posted a screenshot of OpenLP 2.0 and OpenOffice Impress a few days ago, and for an open source application, this is a great pairing. In addition I've also been working on getting PowerPoint Viewer support working in Windows...
"Why?" You may ask. Well there are times when a visiting preacher pops in 5 minutes before the service with his PowerPoint created presentation, and you find that he's using LatestWhizzyUnnecessaryFeature(tm) which just doesn't format correctly in Impress and you don't have time to fix it. Since PowerPoint costs money better spent elsewhere, and native PowerPoint viewer doesn't support dual screen, this hasn't left many options.
So I spent some time trying to automate PowerPoint viewer. This will only work on Windows of course, and since the viewer isn't designed to be automated, it may have the occassional quirk. However I have managed to get basic support working in 2.0 as you probably can't see too well in the small low quality screenshot above!
Also a useful tip for Windows 7 dual screen users. Sometimes you may want to display something on the projector which OpenLP doesn't yet support, maybe a webpage. However dragging it across the screen in full view of the congregation isn't very professional and is a bit hit and miss. I've discovered that Windows 7 has a new key combination to assist with this. If you press the Windows key, the shift key and the right cursor key all at the same time, this will move the current window to the other screen/projector. If you then press Windows key and up arrow, this will maximise the window... although some apps also support "F11" for fullscreen.