Used plumbing...galvanized, even the older black pipe can be saved from the junkyard. Call some plumbers, house renovators, home improvement guys or the handyman ads in your local paper. What you're interested in, is pipes 6' or longer ideally and you can have them threaded at hardware store for cheap if you want to add on for length or to add other fittings for elbows or whatever. Where would this be useful? How about as fence frame, or garden rails for vines, frames for peas or other climbers, straight poles for whatever(6'= 2'in ground 4' for whatever), even framing for a greenhouse, coldframe, or hotbox. Even reused as irrigation pipe, drill small holes and have drip irrigation, or lots of small holes in a line and have a spray pattern over flats in a greenhouse.

You guys are pretty creative so the sky's the limit, what else could they be used for?