I personally use a Hoodman HoodLoupe for Live View use, but today a reader pointed me at the Zacuto Z-Finder, with high quality Schneider optics. The Z-Finder looks very well suited for video use. With many DLSR owners now shooting video, this might just be the ticket.
The Z-Finder is designed to mount and stay there, just as you’d want for video use, but it can also be hung around your neck, snapping into place (a frame attaches around the camera LCD). It sounds interesting, but I haven’t tried one yet.
By comparison, the HoodLoupe is something I hang around my neck, and use as I need it for Live View and/or viewing images after I’ve shot them, especially in bright conditions. See my Feb 11 2008 blog entry for more. The HoodLoupe is
Reader Olivier H recommends the LCDVF, though I haven't tried it: