There are many different sites on the Internet that can assist students, educators, and parents with research, homework, and curriculum design. Some of the best provide free reference materials and services. Here are ten reference sites you can use for your next project without any out-of-pocket costs:

BJ Pinchbeck's Homework Helper - BJ Pinchbeck's Homework Helper is one of the web's most comprehensive reference sites for students. The site links to nearly 1,000 quality sources of homework help and includes a brief description of each.

Infoplease - This free and respected reference site provides an encyclopedia, dictionary, thesaurus, atlas, and other reference works. Infoplease is also a good place to find biographies, timelines, information on current events, and homework help.

Fact Monster - Fact Monster is an Infoplease site with a kid-friendly reference desk. Some of the subjects that can be searched on Fact Monster include people, sports, science, geography, history, world news, and timelines.

The Internet Public Library - The Internet Public Library (IPL) provides an enormous collection of reference materials for students, parents, and teachers. Visitors can browse through subject collections, explore reference works, read newspapers, magazines, or books, and get answers to questions from a real librarian.

World Digital Library - Supported by the United Nations Educational, Scientific, and Cultural Organization, the World Digital Library (WDL) provides primary resources from countries all over the world to scholars, educators, and the general public. Resources are available in a multilingual format and cover a wide range of topics.

Library Spot - Created for educators, students, librarians, and other researchers, this free virtual library brings the best of online reference tools to one easy-to-navigate site. All of the content on Library Spot is hand-selected and reviewed by the site's editorial team

RefDesk - This award-winning, family-friendly reference site serves as a fact checker for the Internet. Offerings include multiple search engines, dictionaries, encyclopedias, almanacs, periodicals, biographies, news sources, weather sources, articles, pictures, and much more.

The Educator's Reference Desk - Created specifically for educators, this online reference desk offers more than 2,000 lesson plans and 3,000 links to education information. The Educator's Reference Desk also provides a decade's worth of answers to questions that have been sent to the AskERIC service.

Virtual Reference Shelf - The Virtual Reference Shelf offers a selection of high quality Internet resources compiled by the Library of Congress. Links lead to reference works, calendars, calculators, consumer information, directories, biographies, and subject-specific information.

INFOMINE - INFOMINE is a librarian-built reference site for students at the university level. A few of the topics covered on INFOMINE include business, economics, government, agricultural sciences, medical sciences, social sciences, math, computing, and the arts.

Guest post from education writer Karen Schweitzer. Karen is the About.com Guide to Business School. She also writes about online degree programs for OnlineDegreePrograms.org.