Schematic Editor - Library files
The microbuilder library http://www.microbuilder.eu/Projects/EagleFootprintLibrary.aspx is pretty good and is maintained by the all around nice guy Kevin Townsend.
There is also the adafruit library https://github.com/adafruit/Adafruit-Eagle-Library

That said, it would probably take no more than 5 minutes to draw that 100 mil header. In my experience Eagle footprints, even the standard ones, are of varying quality and it pays to learn to draw your own.