The list from F'ingHomepage.com is quite good:

Educational/Learning

• khanacademy.org - video lectures on just about any subject
• ted.com - lectures by smart people
• academicearth.org - classroom lectures
• freerice.com - expand your vocabulary while feeding the hungry
• lizardpoint.com - a collection of geography quizzes
• mathrun.net - timed math quizzes
• classicshorts.com - the best short stories
• erowid.org - learn about drugs
• qwikia.com - turn a Wikipedia article into a video
• unplugthetv.com - a collection of intellectually stimulating videos
• factsie.com - a place to learn amazing and unusual historical and scientific facts

Learn Skills

• highercomputingforeveryone.com - learn to program in C
• thechesswebsite.com - a bunch of chess tactics, tutorials, and puzzles
• htmldog.com - learn html
• codecademy.com - learn to code through interactive lessons
• cookingforengineers.com - learn to cook
• digital-photography-school.com - learn photography
• memrise.com - learn a foreign language
• justinguitar.com - guitar video tutorials
• livemocha.com - a language learning community
• musictheory.net - learn music theory
• investopedia.com - learn and practice investing

Useful Web Apps

• mint.com - for budgeting your money
• billshrink.com - compare cell phone and credit card plans
• duckduckgo.com - a search engine that isn’t following you
• padmapper.com - maps out possible apartments/homes that fit your criteria
• zillow.com - another great source for finding your next home
• printfriendly.com - make any webpage print friendly
• printwhatyoulike.com - print precisely what you want from any webpage 
• privnote.com - write a note to someone that will self-destruct after they read it
• freecycle.org - a network of people giving away free stuff in their towns
• couchsurfing.org - crash on someone’s couch anywhere in the world
• recipepuppy.com - search for recipes based on the ingredients you have
• pipl.com - a search engine for finding people
• donorschoose.org - donate to a classroom in need
• charitynavigator.org - evaluates various charities
• govdeals.com - find cheap stuff the government is getting rid of
• newsmap.jp - popular news headlines
• radioreference.com - listen to radio channels across the nation
• jimmyr.com - link aggregator
• msworddit.com - Reddit in Microsoft Word form
• wepay.com - like paypal but less scummy
• thefuckingweather.com - a more profane look at the weather
• wolframalpha.com - a computational knowledge engine
• heavens-above.com - follow satellites and constellations
• whatismyip.com - figure out you I.P. address
• spreeder.com - improve reading speed and comprehension
• simplynoise.com - listen to white noise
• camelcamelcamel.com - tracks prices for any product
• ptable.com - an interactive periodic table
• retailmenot.com - find coupons for just about anything
• searchtempest.com - search all of craigslist with one search
• join.me - peek in on somebody’s computer screen
• thistothat.com - find out the best way to glue this to that
• woorank.com - find out what your website is missing, how you can improve it, and how to make Google recognize it better
• scribblemaps.com - draw on maps then share them with friends
• mailvu.com - video email
• rhymer.com - online rhyming dictionary
• homestyler.com - design your dream home
• wetransfer.com - an easy way to send big files
• mapofthedead.com - shows places around you to help you survive the zombie apocalypse
• pastebin.com - a place to paste text
• idlekeyboard.com - make it sound like you’re hard at work
• wherethefuckshouldigofordrinks.com - find somewhere to get a drink in your area
• dropbox.com - backup your sensitive document online
• seatguru.com - find out where the best seats are on your plane flight
• unlistmy.info - find out which websites store data about you, and tell them to unlist your info
• ifoundyourcamera.net - a collection of lost cameras
• sizeasy.com - check the size of items you buy online
• sleepyti.me - plan out your sleep schedule better
• ninite.com - download all the free software you want at the same time
• ripetrack.com - find out when certain fruits are ripe 
• compassionpit.com - talk out your problems with others, or help others yourself
• paperbackswap.com - swap books with others
• reddpics.com - a look at Reddit’s favorite pictures
• swole.me - plan out your meals better
• weatherspark.com - a graphical look at the weather
• network-tools.com - network tools
• amazon.com - the best place to buy things online
• writecheck.com - correct grammar and check for plagiarism
• wakerupper.com - send yourself a wake-up call
• pcpartpicker.com - plan out your next pc build
• nophonetrees.com - talk to an actual person instead of a machine when you call customer service
• theuselessweb.com - visit random useless websites
• loads.in - find out how long it takes websites to load

Entertainment - Music, Movies, Sports, Books

• redditunes.com - Reddit’s favorite music
• grooveshark.com - great place to listen to tunes
• isitback.com - find out when your favorite television shows come back on air
• literature-map.com - type in an author and they will show you others of a similar style
• runpee.com - find out the best time to run to the bathroom during any movie
• songkick.com - searches your music library and tells you when your favorite musicians play in your area
• midomi.com - sing or hum a song you don’t the name of and it will identify it for you
• slashfilm.com - the best movie news blog on the internet
• nanocrowd.com - find out what movie you should watch next
• page99test.com - read page 99 of a book
• bookseer.com - get recommendations for your next read
• sbnation.com - awesome community of sports blogs
• justthefirstframe.com - just the first frame of today’s webcomics
• music-map.com - find similar musicians
• iwl.com - find which famous writer your write like

Other Interesting Blogs

• thestuffofmen.com - cool stuff every man should own
• artofmanliness.com - learn man stuff
• lifehackninja.com - my blog full of how-to’s and life tips
• thedailymiscellany.com - daily tips, DIYs, ane more
• getrichslowly.org - personal finance advice
• thedatingspecialist.com - seduction tips
• brainpickings.org - a human-powered discovery engine
• fivethirtyeight.blogs.nytimes.com - a look at politics through the numbers
• hackaday.com - a new DIY project every day
• shorpy.com - old and interesting pictures
• boston.com/bigpicture - amazing pictures covering the latest news around the world
• newscientist.com - science news
• uncrate.com - a place for stuff men love
• tastespotting.com - pictures of delicious food
• zenhabits.net - take a breath and read this blog
• foodgawker.com - more pictures of delicious food
• theburninghouse.com - a blog cataloging which possessions people choose to save from a burning home
• dwellinggawker.com - check out how amazing the inside of some homes look
• thesimpledollar.com - more personal finance advice
• veryquiet.com - world news and analysis
• mentalfloss.com - where knowledge junkies get their fix
• mrmoneymustache.com - financial advice through badassity
• studyblue.com - study tips
• lettersofnote.com - personal letters written by famous people

The Science Channel http://www.youtube.com/Best0fScience

Sick Science http://www.youtube.com/SteveSpanglerScience

Veritasium http://www.youtube.com/1veritasium

ASAP Science http://www.youtube.com/asapscience

VSauce http://www.youtube.com/Vsauce

Minute Physics http://www.youtube.com/minutephysics

Brain Scoop http://www.youtube.com/thebrainscoop

Periodic Table of Videos http://www.youtube.com/periodicvideos

Sci Show http://www.youtube.com/scishow

Girl Writes What http://www.youtube.com/user/girlwriteswhat

Smarter Every Day http://www.youtube.com/destinws2