It all really depends on what you're wanting to keep, but IMHO (In My Humble Opinion) there's not much at Home Depot for anything other than the simplest of softies or refuguims...
However, if you're wanting to get a decent amount of quality light over a nano tank, DIY it, and do it as cheap as possible, I highly recommend getting some 36" PC kits from AH Supply:
http://www.ahsupply.com/
I've got one of their 13 watt kits over each of my 6 refuguims, 2 of their 13 watters over my reef as moon lights, and another 2 over my reef as red night viewing lights...
As long as you weren't wanting to keep SPS/Clams/Anemone's or the like, a few of the 36 watt PC's over a 20" nano tank should be quite nice...
(Assuming you're not wanting to go with a 150w MH, of course...

)
Edit - DOH! Just noticed the "Hex" part... Not sure if the 36 watt PC's would work in that scenario. You might could cram a bunch of 13 watt PC bulbs up there, not too sure without seeing it, but I really don't think you're gonna find what you're after at Home Depot... I've tried, believe me...
