For a 48" tank, I think dwarf angels will be a better choice. Small "large angels" can probably be kept also, such as cream or singapore. Bluespotted should be ok too, though I've heard it's not an easy species to keep.
Matt, I do not agree that Navarchus is appropriate for a 48" tank, even for small ones. In addition, small navarchus (juvenile coloration) are known to have difficulty acclimating to captivity. I have a 5" one in my 225G and I can't imagine it being in anything less than a 60" long tank. Navarchus grows very slowly but over the years will reach 8" in the proper environment. I think a 72"x18" 125g (or better yet a 180g) is the minimum for him to live the entire life.