Reef Shop > Floater
Floating Viewer $25 + 9.50 shipping
This little viewing box allows you to see the beautiful corals and invertebrates in your tank. The base is clear, and the walls are black. 5.5" x 5.5" x 3" will fit almost any tank, including those nano systems. It also comes in pretty handy when nuking aiptasia, because you can see clearly where each one hides.
This box may be used for top down photography, but this one would be better.