Six Revisions offer free glossy icon set. It consists of 20 high quality semi-transparent icons. The package also includes 48 derivative icons of the 20 icons. Each icon comes in 6 different sizes (32×32, 48×48, 64×64, 128×128, 256×256 and 512×512) in PNG format.
These icons are free for personal and commercial use. You are not required to attribute the work, although it is very much appreciated. Read the License.txt file included in the download for more information on usage permissions of the files.