There are lot of websites and online tools which can be fruitful for educational purposes. In this modern age, every student and educator should know how to use these websites for their advantage.

The modern marvell called Internet has been a significant part of our lives. Many young peeps start their day with facebook chat and end up in a new movie trailor on YouTube.

Besides being an excellent tool for entertainment and communications, Internet also proves benificial for students. They can get updated information on the go, create slideshows for seminars, make study notes, download reference books for free and do much more on the internet.

Thus, here provided is a short list of 19 most useful websites for students.

1. Wikipedia.com ;
Who doesn't know the biggest online encyclopedia? Wikipedia not only provides basic information on what you search for, but also lists additional resources for extra information on the bottom of the pages. They also provide you images through 'Wikimedia commons'.
 You can also see their sister sites such as Wikiversity, Wiktionary, Commons and Wikibooks.

2. Shorttext.com ;
This website lets you create notes and share them through a uniquelink.

You can format text using simple BBcode, and make hyperlinks.
A similiar site is http://freetexthost.com/

3. Coursera.com ;
This famous e-learning site offers links to free courses on literally anything. You can get training in martial arts or learn a foreign language with ease.
Similiar sites include Alison.com and http://langunita.stanford.edu/

 4. Quora.com:
The world's most popular Q&A site. Users can post their questions and doubts regarding almost anything and get answers from other users.
Quora is also available as mobile app.

Similiar sites include Yahoo! answers (http://answers.yahoo.com/) and
StackExchange.

5. Canva.com :
Canva is an all-in-one image editing toolkit available online. You can make magazine covers, collages, newspaper clippings and much more out of ordinary photos, which are useful for project works .

PicMonkey and Pxlr also provide free online photo editors.

6. Online-Convert.com ;
The all-in-one online file converter helps to convert between audio, video, document, archives, images and other file formats. For example: you can convert a word document into mobile compatible PDF and vice versa. You can also convert an online file found by a URL.

Similiar sites include zamzar.com and convertfiles.com

7. Pixabay.com :
provides a collection of about 600,000 free-to-use stock photos, better suitable for Presentations and project works as well.
PublicDomainArchive.com and pexels.com are some good alternatives.

8. Mega.co.nz
A popular cloud storage site offering upto 50 GB of free storage.
Students can upload, share and download the files on the go.

Dropbox and Google Drive also provide good cloud storage service but offer less
free storage space.

9. Slideshare.net :
a popular presentation sharing site. (currently seems to be owned by LinkedIn). People can share and search for slideshows and presentations on any topic.

10. WikiHow.com :
One of the most popular how-to sites. Provides 'how-to' type definitive articles on literally anything, ranging from 'how to prepare for an examination?' to 'how to earn money online'. 
There you can also get useful advice on a vast array of things by asking contributors through comments.

11. Buddy4Study.com :
A new startup that provides up-to-date information on various scholarships and fellowships, as well as the guidelines to apply for
them. (For Indians)
Alternative: Scholfin

If you want to get information about the scholarships in your country, A Google Search can help a lot.

12. Oregon University's academic success center:
( http://success.oregonstate.edu/ ) - This excellent resource has guidelines and some PDF Whitepapers that teach the way of effective studying. Exam preparation and note taking etc.. issues are also discussed here.

13. TheFreeDictionary.com :
One of the best integrated online dictionaris, this dictionary-cum-thesaurus provides almost all possible meanings and synonyms for the desired word.

14. PDFCrowd.com :
- Helps to save web pages as PDF (portable document format) files for offline reading. Note that PDF files are widely supported on mobile phones while compared to Word or OpenOffice documents.

Similiar sites: PDFmyURL.com, Online2PDF.com

15. Penguin.com :
This is an online library which allows to download famous books in PDF format or as e-books. 
There are lots of alternatives including GutenBerg.org, PlanetPublish.com and http://books.jakhira.com/.

16. Cram.com :
- This amazing website helps you find and / or create online flashcards. Online flashcards help learn, study and remember things better. You can learn a foreign language or prepare for competetive exams using flashcards.

17. HyperBoards.com:
HyperBoards is basically an online forum creation tool. Students can use it to create their own social network or message board between similiar-interested students and share ideas. There are more features and advantages compared to creating a facebook group.

Xobor.com is another free forum creation tool

18. Popplet.com :
It's a famous online mind mapping tool. Mind mapping is an effective study technique and a brainstorming technique as well. It helps to organize information and find relations between concepts.

(If you use an android phone, there are many alternatives. Go to
Google Play and search 'mind mapping'. There are many free mind mapping apps)

19. IDEone.com :
(For Computer science students)
IDE stands for 'Integrated Developement environment'. IDEone is an online sandbox for testing, sharing and debugging snippets of code.

Codepen.io, Github and JSFiddle are some similiar sites.

Conclusion:
It's just a little effort to list some student-useful sites on the web.

Internet provides thousands of educational opportunities in this modern era. We just need to make good use out of it.