Skinks are interesting, but I find them pretty boring.
As mentioned, if the cage is wide enough you can put a beardie in there. BUT. If you get it as a baby you'll have to keep it something smaller at first. A baby bearded dragon would have a helluva time catching crickets and such in a 46 gal. Think something along the lines of a 10 gallon for an outright baby.
THe pluses of a beardie are that they're pretty much the best herp 'pet'. They have quite the personality and are very socialable. And they're fun to watch while they hunt their crickets and such... I would just make sure to do some reading on them before you get one, to make sure you have the tank set up properly.
No other suggestions come to mind right off the top of my head. But I guess it really depends if you want a show piece, something that will hide all the time, or something you can handle a lot.