Highly useful search engines list.

Search engines made a big help to find research papers,informations etc. from internet.Here is a list of most used search engines and some simple tips to use it better.These articles is an updated one,if I find anything new I'll update it.

Google
 The best and biggest search engine.You can search for PDF files by entetering "filetype:pdf" after your keywords.Eg:- nanotube filetype:pdf for word file nanotube filetype:doc You can use this by from  Advanced Search option and select the filetype that you needed.Google supports,Powerpoint,pdf,word (doc),rich text,excel etc.You can restrict your search by choosing Language from advanced search.

Yahoo! Search
 The search engine that helps you find relevant information, video, images, and answers from all across the web.You can use the advanced search option to search for pdf/doc files only by selecting the format that you needed. Eg:-nanotube pdf files only.

Bing (formerly MSN Search and Live Search)
Bing is a search engine that finds and organizes the answers you need so you can make faster, more informed decisions.

Ask.com
Offers search for web sites, images, news, blogs, video, maps and directions, local search and shopping.

Question and answer search
  Now the popularity of yahoo answers shows people need help on their area of research.So here some human answers and automatic answers search engines are shown,these will really helps you.

Human answers search engines

Answers.com
The ultimate answer engine, with quick accurate dictionary, thesaurus, encyclopedia, bios, tech terms, news, sports, weather, and much more.

eHow
  Learn how to do just about everything at eHow, the world's most popular place to find How To instructions.

Uclue
Ask questions and browse existing answers from experts in various categories.

Yahoo! Answers
You can ask questions on any topic, get answers from real people, and share your insights.

Stack Overflow
A language-independent collaboratively edited question and answer site for programmers.                     

DeeperWeb
DeeperWeb is an innovative search engine plugin and an essential Firefox addon for Google.