Logout icon is included into Standard Admin Icons. You can view all icons here:[link]
Each artistic toolbar icon is available in sizes of 16x16, 20x20, 24x24, 32x32, 48x48 and 256x256 pixels. All images are supplied in ICO, PNG, GIF, and BMP formats. Your order will get you all icons in have 256 colors and True Color variants.
Download link: [link]