By default, the NameChk Web app displays results for 82 of what it deems the most popular social networks and websites. You can click Show all below the search box to display all 157 sites it searches.
Results are returned quickly, with each site showing a green available banner or a red taken banner. As an added bonus, NameChk displays a handful of available URLs above the sites it checks for available usernames. Clicking on a site from the NameChk list opens that site in a new tab, and clicking on one of its domain suggestions opens a GoDaddy tab.
The iOS app was released three years ago and has yet to receive an update. I found it functional and fast but a bit buggy.