Finding the invisible web or deep web...

This post concerns the majority of websites and information; those areas which ordinary search engines just don't find because they are not targetting them. It also includes advice on how to search effectively at an academic level. From school to post-grad level this is vital if you don't want to waste your time!

First, the ultimate guide to the invisible web:
 http://oedb.org/library/college-basics/invisible-web

 Secondly, a search engine overview:
http://searchenginewatch.com/article/2066359/Invisible-Web-Database-Search-Engines

Next, learn about how and how not to search for academic purposes:
http://www.vtstutorials.ac.uk/detective/index.html

Then, ten important invisible web search engines:
 http://www.makeuseof.com/tag/10-search-engines-explore-deep-invisible-web/

An example:
 

These lead on to the narrowing down of searches for academic purposes. An excellent categorisation and analysis can be found here: 'Research Beyond Google: 119 Authoritative, Invisible, and Comprehensive Resources'

http://oedb.org/library/college-basics/research-beyond-google

Highly recommended is the Bielefeld Academic Search Engine BASE:
http://www.base-search.net/

Blip TV demonstrates how to use BASE.
http://blip.tv/camosunlibrary/base-bielefeld-academic-search-engine-advanced-search-3537868

After that, consider using a metasearch engine, for example:
 www.metacrawler.com

Nearly there, take a look at these meta and multi-search engines:
 https://www.diigo.com/list/eclark131/Meta+and+Multi+Search+Engines/2lpg04uj4

Finally don't forget about the 314 search engines in other countries:
http://searchenginecolossus.com/ 

Having found your sources, it is important to cite them properly to avoid charges of academic plagiarism. This tells you how:
 http://www.lib.berkeley.edu/instruct/guides/citations.html