Here's the plywood aquarium stand that I'm building for my 55g. The design is my own, based on several other stands that I had seen. I've built some cabinets before when I used to work for a local carpentry company. Originally I picked up a rabbeting bit to frame it with rabbeted edges, but I decided to just do butt joints with 16g finish nails and glue, and some extra plywood to support the corners. There are a few pocket joined corners as well, you'll see in the pictures. Next cabinet I make I'll try out the rabbeting bit.
The entire stand is made 3/4" of maple veneer plywood, except for the doors which will use some 1/4" for the middle paneling. It took about 1.5 4'x8' sheets. I've finished the stand, but haven't made the doors yet.
Total price was about $50 per 3/4" sheet at Lowes, $25 for the 1/4" sheet, and then another $25 for the cabinet hinges, plus glue, nails, pocket screws, and finish.
Tools used were a skil saw, table saw, miter saw, finish nailer, clamps, orbital sander, drill, and a pocket screw jig.
Enough writing, here are some pictures! I'll snap a few more as it looks now, I just need to clean it up. These are from a month ago. I still need to make the doors, and I think I'd like to make a matching hood as well when I have the time.