At work I came across clear pvc piping. You can get it up to 12 inch diameter. I was thinking it would be really cool to have a fish tank that winds around your house. It would be pretty simple to support the pipe. Keeping the sides clean would be the hard part though! You could actually connect two tanks with the pipe if they are the same height. The options are endless! But you better be rich....it's not cheap.
http://www.harvel.com/piping-clear-pvc.asp
http://www.clearpvcpipe.com/index.asp?PageAction=VIEWCATS&Category=19
http://www.harvel.com/piping-clear-pvc.asp
http://www.clearpvcpipe.com/index.asp?PageAction=VIEWCATS&Category=19