The "Seattle Sling" from Camera Armor keeps cameras and other gear free from water, dirt, dust, or cookie crumbs. It's essentially a dry bag inside a padded, single-strap sling, which means you'll have quick access to your gear, but won't be able to take it underwater. Looks useful for adventurey, outdoors shooters, but also seems to take up quite a bit of space.
The Seattle Sling will sell for $150 once they're back in stock. Considering it was just announced that should be any day now. (I'm not sure they were technically ever in stock at their online store.)
Seattle Sling dry bag catalog page [Made-Products.com]