Research Methods Knowledge Base
There is a new online textbook available written by the former president of the American Evaluation Association, Michael Trochim. The intent of this book is to provide students and researchers with information about research and evaluation, including measurement, sampling, analysis, and writing.
The full textbook must be purchased, but there are several subsections which are available at this link.
The planning and evaluation cycle is described here. An overview of several aspects of measurement, validity, reliability, types of measures, research design, and several other topics are available at the site.