Periodic table is the word you might have heard in the subject Chemistry during your schooling. But its not just Chemistry which has a periodic table for certain thing, like the elements.
But there is a periodic table of the Internet which has some of the best websites listed in a categorized manner in various periods and tables.

You would see 18 groups and 7 periods similar to the normal Chemistry elements table, and the various groups represent various categories.

• Group I - Search engines like Yahoo, Google, Live, Ask etc.
• Group II - Internet tools like Firefox, Skype, Gimp etc.
• Group III - Site Ranking like Technorati, Compare.com
• Group IV - Aggregators or Social bookmarks like Digg, Furl etc.
• Group V - Web comics like pbfcomics.com
• Group VI - Productivity like Lifehacker, 43folders etc.
• Group VII - Get Stuff, like ebay and craigslist.org
• Group VIII - Operating systems like Windows, Apple, Ubuntu etc.
• Group IX, X, XI, XII - Miscellaneous stuff like Youtube, Deviantart, Amazon, Slashdot, IMDB, Flickr etc.
• Group XIII - Blogs like Blogger.com, Boingboing etc.
• Group XIV - Social networking like MySpace, Facebook, LiveJournal, Bebo, Orkut etc.
• Group XV, XVI - These are the podcast sites.
• Group XVII - Videos like AskANinja.com, Ted.com etc.
• Group X1V - News websites like CNN, Wikipedia, NYTimes, Wired etc.

Not sure who created this, but its amazing looking and great work. Check the periodic table of the Internet below(click to elnarge) -