A site where I spend most of my time (other than this fair site, of course – indeed, I found this site through that one) is the rather wonderful site TV Tropes – Television Tropes and Idioms, to give it its full name.
For the uninitiated (and that’s rather more of you than I’d like, I suspect), TV Tropes is a site where the conventions of various media are defined (such as the tendency of the black guy to die first in movies) and pages about works that you thought nobody else but you knew about appear with surprising regularity (such as the British show Banzai). Similar in style to Wikipedia (but a lot more relaxed), it’s a fun and absorbing way to spend your time.
But beware, you will lose all your time to this site. Many is the time where I’ve pledged to myself that I will turn off the laptop at a certain time, while there is one tab of TV Tropes open. Several hours later, I finally turn the laptop off, electing to give up on the ones that I have opened by Wiki-Walking, as they call it. I also downloaded a mobile phone application called DroidTropes that lets you mark pages for later reading. As of this writing, I have six pages waiting to be read. I guarantee that I will find two links on each page to read later.
However, this is not necessarily a bad thing. TV Tropes has improved my vocabulary, taught me many useful (and useless) facts about programmes and life in general. For instance, through TV Tropes I learned that Blade Runner was the second DVD ever released (Twister was the first), the phrase “Prince Charming” came from The Picture Of Dorian Grey, and that V.R. (on British postboxes and on Sherlock Holmes‘ wall) stood for Victoria Regina. Hardly facts that nobody has ever known before, I think you’ll agree, but the point is that I learned them and many more through TV Tropes (as I do not tend to take active interests in facts unless I get there through another source).
You have to “Get Known” (make an account) to add examples and edit pages, but this has the advantage of less spam (since the person can be warned away or banned) and it makes it easy to see who did what. I’m sure everyone has an example of a trope in them somewhere. Some of the known Tropers (whether now or in the past) include Irregular Webcomic runner David Morgan Mar and the author Diane Duane. Tropers are encouraged to start pages, but only if you can’t already find them.
The Useful Notes section makes for very interesting reading as well if you can spare the time. Rather than just pages filled with examples, the pages are just descriptions of that subject, elaborated in detail with many useful facts and details that the more casual reader might be interested in knowing. For instance, as far as I recall there is a page on “Cuisines In America” in contrast to the more high-minded Christianity and religious pages. There are also pages on the various gaming and video formats, which are useful if you’re technically minded.
Just in the process of researching this article, I’ve opened seven tabs, so I know what I’ll be doing with the rest of my afternoon. You know what they say: time flies when you’re having fun.