What is safe for GP's to chew on?

The thing that my two guinea pigs chew on the most and is perfectly safe for them is the willow and fruit twig barbell toy by critter ware. They will completely destroy on large one in like 3 - 4 days it's sooo funny. It has a little bell in one end so they like that too. Here is a link to the barbell toybroken link removed)

Stay away from soft woods like cedar, pine and such. Hard woods that are NOT treated and are kiln dried are fine. I've used oak in the past but its not worth it for me to build wood things as they get wrecked to quickly. Wood holds urine, mold(fungus), spores, parasites easier. I like to give my piggies cardboard boxes from kleenexes, cereal and the corragated stuff too. When it gets yucky it gets pitched without guilt. You can give them branches from trees and make your own twig things. Apple tree branches are prefered. Do NOT use trees that have pitted fruits like cherrys as the branches have a toxin in them that would harm the piggies.

There are so many things you can do for them without spending a whole lot. A handful for fresh chem free grass in a paper bag is a fav!!!