Google Fonts - Making the web more beautiful, fast, and open through great typography
Font Viewer - Font Viewer is an application which does exactly that - it views fonts!
FontJoy - Get smart font pairings in one click
NexusFont - Choose and manage your fonts with Nexus Font.
Better Google Font Finder - Sort & compare Google Fonts by their visual attributes.
Font Manager - Simple font management for GTK+ desktop environments