I was at a friend's place in Portland and they had this whole wall of floating shelves they built with just a 2x4 and some pipe flanges. | DIY Home Projects - The Community Guide
Those pipe flange shelves are a classic for a reason. They look way more expensive than they are, and the build is dead simple if you can use a drill. The real trick is getting the pipes level and making sure you hit the studs. A cheap laser level saves a ton of headache. You can stain the wood or leave it raw for a more industrial look.
I used to think they looked too much like a dorm room project. Then I saw my friend's set with black pipes and a dark walnut stain, and it completely changed my mind. It looked so polished and solid, nothing like the basic pine boards I pictured.