My simple version is shown below, just two cheapo clamps hot glued and zip tied end to end. Great for holding plants steady, holding small fill or black cards or other miscellaneous things.
If you google "plamp" you'll come up with a number of diy versions as well as the ready made Wimberly "Plamp". There's a few options for a flexible but rigid arm with a clamp at either end, one that looks like a giant twist tie,
DIY Plamp #1 | Flickr - Photo Sharing!, or one made from LocLine that looks more like the Wimberly version,
DIY Mega-Plamp (aka Blamp) - FM Forums.
There's also the ready made 'NastyClamps', but they're probably overkill for holding lightweight plants in the wind.