The oblong green element used in several of these centerpieces is called rush, horsetail or the genus name Equisetum (pronounced /ˌɛkwɨˈsiːtəm/). The variety shown in these pictures is a very thick stalk, usually it is very skinny. I actually have a garden of it in my front yard, it is wonderful linear plant specimen that multiplies. To learn more about this facscinating plant click this link http://en.wikipedia.org/wiki/Horsetail.
The grape vine log is actually a very old portion of grape vine plants. The below image has been sand blasted to give it a light color. Lucky bamboo, sheet moss and Thistle add some character to a interesting piece of wood.
White dendrobium orchid blossoms are clustered together to create great textures with the blue Thistle and rush.
White Phalenopsis Orchids always make for a dramatic statement. In my opionion they are often used in centerpieces with other elements that crowd out the beauty of the stunning blossoms.