The following site is a collection of high quality websites carefully selected, described, and organzied by a team of librarians. There is a specific section called "Ready Reference and Quick Facts" which is a handy guide to just many reference sources.

Librarians' Internet Index (http://search.lii.org/index.jsp?more=SubTopic10)

Thanks..
Very useful when we need to answer a thread..

You are very welcome!