It’s not that often where icons by themselves can be looked at as a work of art. Henry Jones over at WebDesignLedger has compiled a list of twenty-two different icon sets but these are no ordinary icon sets. These particular icons specialize in being extremely detailed. One of my favorites from the list is the NES Icons Pack created by DeviantART member Ahuri.
The compiled list does not contain information regarding how these particular icons can be used so be sure to read that information on the icon sets respective home page.