my wife hates the fact that you can see the pump/heater wires and wall through the tank. appart from the obvious sheet backgrounds, what do you use to cover the back whilst making the tank look atractive.
i just finished making mine tonight. i used a book of paper from the craft store. its the type of paper usually used for writing on with silver gel pens.
My LFS have those 3d backgrounds in and they look really good but they are quite expensive. They appear to be made out of some kind of sponge material.
I have a back to nature 'Rocky Juwel' in my Juwel RIO 125... ...they look fantastic (see my posting under 'pictures of users tanks') but are expensive:
Mine cost (gulp) £120! But it is well worth it.
The Juwel backgounds are also pretty good but also work out at c. £50 for a 125 Ltr tank.
I realise not everyone will be willing to spend this type of money on a background (also not very DIY)... ...but they are worth saving for... ....that and a Playstation 3
I got a picture of the Mekong river I took in Laos (It has river and trees and bue sky with clouds) and blew it up and laminated it and used it as the background for one of my betta tanks. It looks pretty cool and the river is from the same part of the world as the fish so it suits.