There is a whole new generation of projection units that use similar imaging components as the LCD rear projection sets, but are optimized for much better contrast. Granted, you can't use them outside but their indoor performance is just short of amazing. They're nothing at all like the units you see at presentations and the screens need to be either pulled taut on a frame or mounted to the wall like wallpaper for the best effect.

Find a local high-end AV shop and check them out. Toshiba has one that just came out with an advertised contrast that rivals direct view. That's a long way from PowerPoint!