I get to try a lot of cases, and I'm rarely impressed, but one case maker at CES hit the right mix with their wood-backed cases that use a polymer interior. The problem with 100 percent wood or bamboo cases is they can chip, crack, or respond to humidity and lose their ability to safely hold your iPhone.
The cases from LAX Gadgets use a traditional soft polymer for the part that touches your iPhone, and the back has a beautiful real wood layer. Choose from light or dark wood, with numerous variations of each. At CES, they even showed off versions with images burned into the wood! The cases are rigid, protective, and still have the organic feel that only real wood can offer.