DEVEST8R-
Mr. Aqua's got some really neat smaller tanks...I think my favorite's their ~12 gallon 3' long one. Is that the one you're talking about? If so, maybe getting three smaller panes of glass cut to 12" x and using some soft silicone bumper feet (look at Target or Lowe's) to hold it 1/16 or so off the rim without sliding would work. Don't forget to get the edges bevelled and have a small hole cut for easy opening and air circulation.
HiImSean's got a point about the mesh top and keeping that rimless look...on several sites there's mesh covers that look pretty good, usually that rely on velcro or clips at the tank's corners. And then there's others that really look...special. It's not my preference, but it can be done well and is visually striking.
I guess it depends on your concerns and personal taste. Controling temp/salinity swings, preventing carpet surfers or all of the above? On my 9 gallon aquastyle the glass top seems to just cut down on heat loss, rather than fostering heat buildup (plus it keeps top-off needs to something sane for something that small).