Been doing some research on web monetizing and SEO business in the past 2 months. Here's a look at some of the popular sites, what's their content, their traffic rank.
The following data is based on alexa.com.
reach rank alexa URL (site content; type) 0.00156 105k modularsystems.sl (Second Life Emeral Viewer) 0.00202 112k staynalive.com (seo) 0.0026 79k xahlee.org (math, programing, gallery, social commentary) 0.0029 72k jensense.com 0.00311 66k writetodone.com (writing tips blog) 0.00358 57k skelliewag.org 0.0043 46k terrydean.org 0.00451 43k cryptome.org (politics, whistle-blower) 0.00529 35k decor8blog.com (home deco blog) 0.0068 32k webdesign10.com (web dev tips) 0.0108 16k webhostingsearch.com (webhosting search) 2010-04-14 0.00661 14k xstreetsl.com (Second Life estore) 0.0076 24k microformats.org (comp tech; ref; tutorial) 0.0109 17k outspokenmedia.com (seo; Rhea Drysdale) 0.0197 9k zenhabits.net 0.0238 8k ask-leo.com (Windows tips blog) 0.0238 7k swik.net (online bookmark) 0.0588 2k fark.com (lurid news portal; soft porn; shock) 0.0672 2k labnol.org 0.0668 1.9k seomoz.org (seo; Sarah Bird) 0.0773 2k problogger.net (seo, blogging) 0.0791 2k makeuseof.com (computer use tips) 0.307 0.357k w3schools.com (web programing)
The first number is the site's “reach” of the past 3 months, defined by Alexa as the fraction of readers of the site with respect of all internet users. Higher the number means more popular. For example, if reach is 0.001, that means 0.1% of internet users visits the site. (multiply the number by 100 to get a percentage.)
The second number is the rank of the site. So, 2k means the site is ranked at 2000 of all websites, by popularity. Note that rank can change a lot from month to month, so is not very reliable figure for popularity. For example, on some months, my site xahlee.org is ranked 50k, but in other months, it's 70k, a difference of 20k, even though the visitors only increased or decreased about 1k or 2k.
Also, last i checked in ≈2008, alexa under-estimated my site's traffic by perhaps 20% less from actual.
The link is to alexa's data on the site. You can visit the site to see what the site actually is, from a link there.
The text in parenthesis is a rough remark about what the site do.
These data are from alexa as queried sometimes in April.
Based on my study, my site can generate USD $1k ad revenue per month. From that, one can guess how much other sites are making.
For example, my site has a reach of 0.0026. The site problogger.net has a reach of 0.773. That's 297 times more. So, $1k times 297 is $297k. Well, that's way off. Problogger guy makes 6 digits yearly from 2 of his sites. Assume he makes 100k per year just from the problogger site. That's ≈8.3k per month, not 297k. The relation of site's traffic and its ad revenue potential isn't linear. Doubling the traffic will certainly not double the income.
It's is hard to estimate how much each site makes, because there's lots variables, how aggressive they advertise if at all, their reader type, their content type, etc. But, given a site's traffic, a estimate of ad revenue is certainly possible. There's quite a few sites dedicated to providing this info. (See: How To Be A Online Ad Publisher (Monetize Your Website))
(If you are a advertiser, please advertise on my site. I give you the best ad effectiveness price ratio. See: Advertising XahLee.org.)
In 2008, i've also done a survey on popularity of computer programing related sites. See: Computer Language Websites Popularity.