Right now I am using contact paper as a background. Lots of different ways to go with it and, you get a whole roll for around $3.00 and it does ALL my tanks (10 gallon, 2 - 5 gallon, 2 gallon) with LOTS left over.
I also have been looking at the stuff to etch glass. You would have to get a seperate piece of glass though I think. Still don't know about that. Also seen some spray that frosts glass that would be kinda neat.
I think the fish net would look awsome. Post us a pic whenever you get done!