I've been on both sides of this - as tech and as on-stage presenter (as well as in the audience), and I don't really see a need for an enclosure or a special stand. I've always just used nice looking monitors. So long as they can tilt a bit (it doesn't have to be much), the presenter can see them fine, unless he is standing right at them. Tape the cords tight to the monitor's stand, and the whole thing is sleek enough and unobtrusive. Depending upon the stage size, I've used everything from a 17" monitor to a 30" monitor for this. As long as they're only using it for confidence (and not for actually reading their slides as they go), any of these should be fine.
One caveat: I always tape the stand down. If it's not a _very_ stable stand, I have even been known to make an auxiliary base (thin plywood, painted black) that is attached with whatever works for the situation (screws, carpet tape, zip ties, etc.).
