SparkFun has an Eagle library that has pads for single and dual row 0.1" headers from 1 to 40 pins. Here is one of several 1x03 headers (single row, three pins):
Their library SparkFun.lbr can be downloaded here. It works with both version 5 and version 6 (I haven't tried it on version 7 yet). They also have a set of libraries in the new XML format (version 6 and later) here.